Maraging steel is one of typical high strength steels used for light-weight mechanical structures due to its significantly high strength over 2000 MPa. It was melted in vacuum furnace in order to reduce the contents of unexpected inclusions so that higher mechanical properties can be achieved. After solution treatment, appropriate aging treatments were applied to some specimens to provide the desired strength levels. Ultra-long life fatigue properties were investigated by using both solution treated and aging hardened specimens under rotating bending fatigue. The effects of aging conditions were examined from the viewpoints of fatigue life, strength distribution, fatigue mechanism, and fracture morphology.