Microsoft does not include Ajax controls in Visual Studio. You need to install Ajax Control ToolKit differently. Here in this Article I will explain how you can install Ajax Control ToolKit. To do that first you need to download Ajax Control ToolKit from CodePlex. Then go to Downloads Tab & select your preffered version like for Visual Studio 2008 download Ajax Control Toolkit for .NET 3.5. If you are using Visual Studio 2010 then you can use either the .NET 4 or .NET 3.5 versions of the Ajax Control Toolkit.
After download the required version of Ajax toolkit open the downloaded file and extract all the files. Now open Visual Studio and create a new ASP.NET website. Open Default.aspx page. Now open Toolbox in visual studio and create a new Toolbox tab by right clicking the Toolbox and selecting Add Tab. Name the new tab “Ajax Control Toolkit”. Right click beneath the newly created “Ajax Control Toolkit” tab and select the menu option “Choose Items”. Click the Browse button and browse to the folder where you extracted the Ajax Control Toolkit. Pick the “AjaxControlToolkit.dll” and click the OK button to close the Choose Toolbox Items dialog. Now if we check Toolbox then we will found Ajax Toolkit tab contains all controls like below:
Now you can use Ajax controls as per your requirement.