*.aspx Page include into header 

<script type="text/javascript" src="ckeditor/ckeditor.js"></script>
    <script type="text/javascript" src="ckeditor/adapters/jquery.js"></script>

include into body 
 
<textarea name="editor1" id="ckeditor"></textarea>
<input id="hidCKEDitorValue" type="hidden" runat="server" />
<asp:RequiredFieldValidator ID="RequiredFieldValidator1" ControlToValidate="hidCKEDitorValue" Display="Static" SetFocusOnError="true" runat="server" ErrorMessage="* required"></asp:RequiredFieldValidator>
 <asp:Button ID="imgSaveBottom" runat="server" OnClick="Create_Click" Text="Save" OnClientClick="javascript:return GetCKEditorData();" />

<script type="text/javascript">
        $(document).ready(function () {
                    $('#ckeditor').ckeditor(); 
                    $('#ckeditor').val($("#<%= hidCKEDitorValue.ClientID %>").val());  
                    }
                    );        
                    
         function GetCKEditorData() {
            var data = $('#ckeditor').val(); 
            if (data != "") {
                $("#<%= hidCKEDitorValue.ClientID %>").val(data);
                return true;  
            } 
            else 
            {
                alert("Empty is not allowed.");
                return false;
             }
                     
          }  
 </script>

*.aspx.cs page 

protected void Create_Click(object sender, EventArgs e)   
{
    String ckContentValue=hidCKEDitorValue.Value.Trim();    
}