1//jQuery 1.6+ use
2$('.checkbox').prop('checked', true);
3//jQuery 1.5.x and below use
4$('.checkbox').attr('checked', true);
1//jQuery 1.6+ use
2$('.checkbox').prop('checked', true); //false for uncheck
3//jQuery 1.5.x and below use
4$('.checkbox').attr('checked', true); //false for uncheck
1//For jQuery 1.6 and above
2$('#myCheckBoxID').prop('checked', true);
3//For jQuery Before 1.6
4$('#myCheckBoxID').attr('checked','checked');