Abstract: A midsole having a bellows type of shock absorbing air bag and a method for preparation of such a midsole. The present midsole comprises a hexahedral-shaped air bag for absorbing an outer shock and comprising upper and lower parts which are provided with a plurality of vertical bellows members, a plurality of elastic bodies for providing elasticity for the air bag and being received in each bellow member, a plurality of upper and lower caps for causing the elastic bodies to maintain their positions in the bellows members and being mounted on the air bag as engaging with an open end of each bellows member, an air control valve for controlling air charge in or air discharge from the air bag and an air communication pipe for permitting the air bag to communicate with the air control valve by being connected at an end thereof to the air bag and at the other end to the air control valve.