The hydrogen content in γ-Fe2O3 was determined by thermal neutron transmission method. The phase transformation of γ-Fe2O3 was studied with D. T. A., magnetic analysis and Mossbauer effect. The presence of hydrogen in the crystal structure of γ-Fe2O3 was ascertained by the experimental results. The crystal structure of γ-Fe2O3 become more stable and the transformation temperature from γ-Fe2O3 to α-Fe2O3 will increase when the cation vacancy of γ-Fe2O3 was occupied by H1+, Co2+, Si4+, P5+ ions etc.