The fatigue fracture characteristic of a commercial MS1700 martensitic advanced high strength steel in a hydrogen environment was investigated. Flat, unnotched specimens were subjected to fatigue loading until failure in three different environments: (i) air, (ii) 0.1M NaOH solution at -1700 mVHg/HgO and (iii) 3.5% NaCl solution at -950 mVAg/AgCl. The fatigue testing conditions were: (i) frequency of 1 Hz, (ii) load ratio of 0.1, and (iii) mean stress equal to 50% of yield strength. Fractographic analysis was conducted on failed specimens to determine the differences in fracture surface morphology, and the reduction of area was calculated to measure changes in ductility. Results showed the detrimental influence of hydrogen on the fatigue life, ductility and fractography of MS1700 charged in 0