Hi Yuriy,
I have attached the sample that display's the state of the check box when the checkbox is checked or unchecked in the HtmlUI control. The checked Attribute of the checkbox control is used to determine whether the check box is checked or not.
Please have a look at the sample and let me know if you have any queries.
http://websamples.syncfusion.com/samples/HTMLUI/f66230//main.htmThank you for your interest in Syncfusion products.
Regards,
Ramu