Hydrogen accumulation during fatigue of bake-hardened Al-Mg-Si alloys was investigated by means of hydrogen microprint technique. As a result of S-N curve relation as a function of testing frequency, effect of environmental hydrogen on fatigue properties was not clearly identified. Based on the low cycle fatigue test with 60MPa stress amplitude, it was revealed that hydrogen was preferentially accumulated on slip lines and that distribution of hydrogen emission was changed in the crack propagation direction. Hydrogen was preferentially accumulated at the coarse slip lines near the fatigue cracks where the separation of slip planes was observed in the fracture surface. On the other hand, hydrogen was observed on the slip lines arranged like steps where the fatigue striations were formed in the fracture surface. At near the final fracture area where the finer slip lines were formed on specimen surface, hydrogen was arranged on each slip lines formed by multiple slips. Morphology of hydrogen accumulation on slip lines was not changed when the testing frequency was changed from 2Hz to 15Hz.