Provided is a drainage structure for an electrical connection box capable of preventing an internal circuit board from getting wet even if water has entered. An electrical connection box main body is mounted on a vehicle wherein a main body-side connector is located on an upper side and protrudes from an opening in a horizontal direction, and a protruding end portion of a housing peripheral wall of a lateral electrical component attaching portion protrudes to the outside from a lateral window, the lateral electrical component attaching portion protrudes laterally from on a side edge portion of a circuit board. A first drainage channel is provided inside the electrical connection box main body, and a second drainage channel extends downward and having an upper end portion connected to the first drainage channel in the protruding end portion of the housing peripheral wall of the lateral electrical component attaching portion.