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RegularExpressionValidator.ValidationExpression Property

Gets or sets the regular expression that determines the pattern used to validate a field.

Namespace:  System.Web.UI.WebControls
Assembly:  System.Web (in System.Web.dll)

public string ValidationExpression { get; set; }
<asp:RegularExpressionValidator ValidationExpression="String" />

Property Value

Type: System.String
A string that specifies the regular expression used to validate a field for format. The default is String.Empty.


The regular expression is not properly formed.

Use this property to specify the pattern used to check for predictable sequences of characters, such as those in social security numbers, e-mail addresses, telephone numbers, and postal codes.

The RegularExpressionValidator does not perform validation on an empty string. If the string you are testing might be empty, use the RequiredFieldValidator as well as the RegularExpressionValidator.

For more information on regular expressions, see .NET Framework Regular Expressions.


If you experience problems with pattern matching constructs, try wrapping the expression with "^(" and ")$". For example, "a|ab" becomes "^(a|ab)$".

This property cannot be set by themes or style sheet themes. For more information, see ThemeableAttribute and ASP.NET Themes and Skins.

Walkthrough: Validating User Input in a Web Forms PageBuilding ASP .NET Web Applications in Visual Studio

The following example demonstrates how to use the ValidationExpression property to validate a field with five numeric digits. When the Button control is clicked, the resulting OnClick event handler checks the IsValid property of the Page to determine whether the text in the TextBox satisfies the regular expression.

Security noteSecurity Note

This example has a text box that accepts user input, which is a potential security threat. By default, ASP.NET Web pages validate that user input does not include script or HTML elements. For more information, see Script Exploits Overview.

<%@ Page Language="C#" AutoEventWireup="True" %>

 <!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN"
<html xmlns="" >
    <title>RegularExpressionValidator Example</title>
<script runat="server">

       void ValidateBtn_Click(Object sender, EventArgs e) 
          if (Page.IsValid) 
             lblOutput.Text = "Page is Valid.";
             lblOutput.Text = "Page is InValid.";


    <form id="form1" runat="server">

    <h3>RegularExpressionValidator Example</h3>

       <table style="background-color:#eeeeee; padding:10">
          <tr valign="top">
             <td colspan="3">
                <asp:Label ID="lblOutput" 
                     Text="Enter a 5-digit ZIP Code" 

             <td colspan="3">
                <b>Personal Information</b>
             <td align="right">
                Zip Code:
                <asp:TextBox id="TextBox1" 
                <asp:RegularExpressionValidator id="RegularExpressionValidator1" 
                     ErrorMessage="ZIP code must be 5 numeric digits"
                <asp:Button text="Validate" 
                     runat="server" />


.NET Framework

Supported in: 4, 3.5, 3.0, 2.0, 1.1, 1.0

Windows 7, Windows Vista SP1 or later, Windows XP SP3, Windows XP SP2 x64 Edition, Windows Server 2008 (Server Core not supported), Windows Server 2008 R2 (Server Core supported with SP1 or later), Windows Server 2003 SP2

The .NET Framework does not support all versions of every platform. For a list of the supported versions, see .NET Framework System Requirements.