Very sturdy! Great for my 20lb cat, although I did add some weight to the bottom to add stability. I’ve never had to worry about it topping over or not supporting my baby’s weight. Only down side is the “steps” - or second piece from the top that extends - doesn’t extend far enough. The steps on either side are just too short and don’t offer enough platform for my cats. So instead of using that to help them get down from the top, they just jump down straight from the top story. This is a concern with older/fatter cats and their joints.