A building block includes a hollow brick and a power supply base. The brick has at least two studs extended from a top thereof, at least two tubes corresponding to the studs defined in a bottom thereof and at least two electricity connection units corresponding to the studs disposed therein. The electricity connection unit has a rod connected with a positive conducting member and a negative conducting member. A light member is connected with the positive and negative conducting members. A first positive contact and a second positive contact are respectively located at two ends of the positive conducting member, and a first negative contact and a second negative contact are respectively located at two ends of the negative conducting member. The light member generates light when the bricks are connected to each other by engaging the studs with the tubes.