Abstract: A mask and a mask assembly, which relates to the display field. The mask includes an opening region, a welding region and a blocking groove, the welding region is arranged around the opening region, and the blocking groove is arranged outside the opening area. When the mask is welded to a frame, wrinkles will appear on the mask. In embodiments of the present application, by providing a blocking groove on the mask, the spreading of the wrinkles may be blocked by the blocking groove, thereby preventing the wrinkles from extending into the opening region of the mask, avoiding the position shifting of the opening region, and improving the evaporation accuracy.