A first connector and a second connector of this connector assembly can mutually connect along the vertical direction. The first connector comprises a first housing provided with a sliding surface, a locking surface, and a receiving surface. The locking surface intersects, at an angle of 90° or less, with a line segment extending straight upward from the locking surface. The second connector comprises a second housing provided with a spring section and a locked section. The locked section can move forward and backward as the spring section elastically deforms. The locked section has a locked surface. When the second connector is in a separated state of being separated from the first connector, the locked surface intersects, at an angle of 90° or less, with a line segment extending straight upward from the locked surface. In a fitting step, the locked section moves downward while being pressed against the sliding surface. The locked section abuts the receiving surface upon moving downward on the sliding surface.