diff --git a/src/components/01_branch-management/FormBranchInformation.vue b/src/components/01_branch-management/FormBranchInformation.vue
index 28fd6004..9c8e0607 100644
--- a/src/components/01_branch-management/FormBranchInformation.vue
+++ b/src/components/01_branch-management/FormBranchInformation.vue
@@ -155,7 +155,7 @@ function formatCode(input: string | undefined, type: 'code' | 'number') {
               ? $t('branch.form.headofficeNameEN')
               : $t('branch.form.branchNameEN')
           "
-          :rules="[(val) => val && val.length > 0]"
+          :rules="[(val) => val && /^[A-Za-z]+$/.test(val)]"
           :error-message="$t('form.error.required')"
           for="input-name-en"
         />
diff --git a/src/components/02_personnel-management/FormPerson.vue b/src/components/02_personnel-management/FormPerson.vue
index 4135c00a..58345721 100644
--- a/src/components/02_personnel-management/FormPerson.vue
+++ b/src/components/02_personnel-management/FormPerson.vue
@@ -217,7 +217,11 @@ watch(
           class="col"
           :label="$t('personnel.form.firstNameEN')"
           v-model="firstNameEN"
-          :rules="[(val: string) => !!val || $t('form.error.required')]"
+          :rules="[
+            (val: string) => !!val || $t('form.error.required'),
+            (val: string) =>
+              /^[A-Za-z]+$/.test(val) || $t('form.error.letterOnly'),
+          ]"
         />
         <q-input
           :for="`${prefixId}-input-mid-name-en`"
@@ -242,7 +246,11 @@ watch(
           class="col"
           :label="$t('personnel.form.lastNameEN')"
           v-model="lastNameEN"
-          :rules="[(val: string) => !!val || $t('form.error.required')]"
+          :rules="[
+            (val: string) => !!val || $t('form.error.required'),
+            (val: string) =>
+              /^[A-Za-z]+$/.test(val) || $t('form.error.letterOnly'),
+          ]"
         />
       </div>
 
diff --git a/src/components/upload-file/FormCitizen.vue b/src/components/upload-file/FormCitizen.vue
index 02e55179..c15b0b64 100644
--- a/src/components/upload-file/FormCitizen.vue
+++ b/src/components/upload-file/FormCitizen.vue
@@ -310,6 +310,8 @@ function formatCode(input: string | undefined, type: 'code' | 'number') {
             :label="$t('customer.form.firstNameEN')"
             for="input-first-name-en"
             v-model="firstNameEN"
+            :rules="[(val) => /^[A-Za-z]+$/.test(val)]"
+            :error-message="$t('form.error.letterOnly')"
           />
           <q-input
             dense
@@ -320,6 +322,8 @@ function formatCode(input: string | undefined, type: 'code' | 'number') {
             :label="$t('customer.form.lastNameEN')"
             for="input-last-name-en"
             v-model="lastNameEN"
+            :rules="[(val) => /^[A-Za-z]+$/.test(val)]"
+            :error-message="$t('form.error.letterOnly')"
           />
 
           <q-input
diff --git a/src/pages/03_customer-management/components/employer/EmployerFormAbout.vue b/src/pages/03_customer-management/components/employer/EmployerFormAbout.vue
index 6b06aec5..cef82f6a 100644
--- a/src/pages/03_customer-management/components/employer/EmployerFormAbout.vue
+++ b/src/pages/03_customer-management/components/employer/EmployerFormAbout.vue
@@ -105,6 +105,8 @@ defineProps<{
         :label="$t('customer.form.registerNameEN')"
         for="input-register-name-en"
         v-model="registerNameEN"
+        :rules="[(val) => /^[A-Za-z]+$/.test(val)]"
+        :error-message="$t('form.error.letterOnly')"
       />
 
       <q-input
diff --git a/src/pages/03_customer-management/components/employer/EmployerFormBasicInfo.vue b/src/pages/03_customer-management/components/employer/EmployerFormBasicInfo.vue
index d4966a1c..868cb064 100644
--- a/src/pages/03_customer-management/components/employer/EmployerFormBasicInfo.vue
+++ b/src/pages/03_customer-management/components/employer/EmployerFormBasicInfo.vue
@@ -344,6 +344,8 @@ function formatCode(input: string | undefined, type: 'code' | 'number') {
         :label="$t('customer.form.firstNameEN')"
         for="input-first-name-en"
         v-model="firstNameEN"
+        :rules="[(val) => /^[A-Za-z]+$/.test(val)]"
+        :error-message="$t('form.error.letterOnly')"
       />
       <q-input
         dense
@@ -354,6 +356,8 @@ function formatCode(input: string | undefined, type: 'code' | 'number') {
         :label="$t('customer.form.lastNameEN')"
         for="input-last-name-en"
         v-model="lastNameEN"
+        :rules="[(val) => /^[A-Za-z]+$/.test(val)]"
+        :error-message="$t('form.error.letterOnly')"
       />
     </div>
 
diff --git a/src/pages/03_customer-management/components/employer/EmployerFormBusiness.vue b/src/pages/03_customer-management/components/employer/EmployerFormBusiness.vue
index 76d4e745..89e486f5 100644
--- a/src/pages/03_customer-management/components/employer/EmployerFormBusiness.vue
+++ b/src/pages/03_customer-management/components/employer/EmployerFormBusiness.vue
@@ -174,6 +174,8 @@ let jobPositionFilter = selectFilterOptionRefMod(
       class="col-md-6 col-12"
       :label="$t('customer.form.jobPositionEN')"
       v-model="jobPositionEN"
+      :rules="[(val) => /^[A-Za-z]+$/.test(val)]"
+      :error-message="$t('form.error.letterOnly')"
     />
 
     <q-input