The effect of hydrogen on mechanical properties and superplastic deformation of two commercial beta titanium alloys, Ti-4Al-7Mo-10V-2Fe-1Zr(Ti-471021) and Ti-10V-2Fe-3Al (Ti-1023), was studied in the range of hydrogen concentration up to 1.3wt%. The elevated temperature hardness of Ti-471021 alloy increased with hydrogen concentration. The stress levels during the superplastic deformation in both alloys increased with increasing concentrations of hydrogen in the P-phase region. X-ray diffraction results and examination of the microstructure with TEM revealed that no hydrides had formed up to hydrogen concentrations of 1.3wt%. The increase in flow stress was mainly due to the solid solution strengthening by hydrogen during the superplastic deformation.