A connector assembly comprises a first connector and a second connector mateable with each other. The first connector comprises two first positioning portions each having a first outer surface, and the second connector comprises two second positioning portion each having a second outer surface. Under a mated state where the first connector and the second connector are mated with each other, the first outer surfaces face the second outer surfaces in a horizontal direction (Y-direction), respectively. The connector assembly comprises at least one of a pair of first depressions provided to the first positioning portions, respectively, and another pair of second depressions provided to the second positioning portions, respectively. For example, when the first positioning portions are provided with the first depressions, respectively, under the mated state, each of the first depressions is located below an upper end of the first outer surface and depressed inward in the horizontal direction.