1. Set EnableScriptGlobalization=true on the script manager <asp:ScriptManager runat="server" EnableScriptGlobalization="... /> 2. Use the Sys.CultureInfo.CurrentCulture command either inside the alert or through Firebug console to check the CultureInfo at the client side 3. use Number.parseLocale instead of pareFloat so that it get correct value according to the current culture. 4. to update the value back with current culture use localeFormat <script type="text/javascript"> function ......