To provide a vehicle body side part structure at low cost and having an extremely simple structure, greatly improved in its accessibility to a rear seat, and capable of protecting occupants upon collision from the side without increasing the door weight.

This structure comprises: a first opening part 2a for an occupant of the front seat 5 to get in and out, provided on the front seat 5 side of a side wall of the vehicle body; a second opening part 2b smaller than the first opening part 2a provided on the rear seat 6 side at the back of the front seat 5 or on the luggage compartment side, in the back of the first opening part 2a; a pillar extending in a vertical direction forming a rear end of the first opening part 2a and a front end of the second opening part 2b; and a door 3 mounted openably/closably to close the first and second opening parts (2a, 2b). The structure is characterized in that the first and the second opening parts (2a, 2b) open with one opening operation of the door 3.