The question is the title. The ATX motherboard size is 12" x 9.6" and the micro ATX case is 16.6" x 10.9" x 14.5". So I would think it could fit. Would the expansion slots line up or something?
Nope...ATX are full size boards. You can't fit them into a smaller space, but can fit smaller boards (micro-ATX) into a bigger space - just like Hunter said