Validation Check Boxes Using JavaScript

 if (aspnetForm.ctl00$PlaceHolderMain$ddlKaizenCategory != "--Select Category--") {  

                var chkListModules = document.getElementById('<%= cblBenefitCategory.ClientID %>');  

                ////debugger;  

                var chkListinputs = chkListModules.getElementsByTagName("input");  

                for (var i = 0; i < chkListinputs.length; i++) {  

                    if (chkListinputs[i].checked) {  

                        args.IsValid = true;  

                        return;  

                    }  

                }  

                args.IsValid = false;  

            }  

    

        }  

Simple Another Way: 

protected void btn_click(object sender,EventArgs e) { foreach(GridViewRow row in Gv.Rows) { if(((CheckBox)row.FindControl("chk")).Checked==true) { //do stuff on here } } }