There are two ways to achieve this. 1. Directly from Code Behind 2. Using Regular Expressions
1. Using Code Behind :
if (decimalValue > 0)
{
}
2. Using Regular expression :
<asp:TextBox runat="server" ID="textDecimal" ></asp:TextBox>
<asp:RegularExpressionValidator runat="server" ID="rexDecimal" ValidationExpression="^\s*(?=.*[1-9])\d*(?:\.\d{1,5})?\s*$" ControlToValidate="textDecimal" ErrorMessage="Invalid"></asp:RegularExpressionValidator>