A cart capable of being horizontally folded without increasing the height having a frame composed of a front wall, a back wall and two symmetric side walls, a chassis disposed at the bottom of the frame, and four wheel assemblies disposed on two sides of the front wall and two sides of the back wall respectively, wherein the front wall comprises an n-shaped support, a lower horizontal tube and two sliding blocks, the lower horizontal tube is fixed to two symmetric ends of the n-shaped support, the sliding blocks are disposed along two vertical tubes of the n-shaped support and are able to slide upwards and downwards; the back wall is identical in structure with the front wall.