We present herein the effects of hydrogen on the microstructure of surface layers of two-phase titanium Ti-6Al-4V alloy. We describe the damage caused by hydrogen and the possibilities of using hydrogen as a temporary alloying element. The paper regarding the HTM - Hydrogen Treatment of Materials as an attractive method for controlling microstructure and improving final mechanical properties of titanium alloys. Hydrogen treatment consists of three stages: hydrogenation in a hydrogen gas atmosphere (600 °C), cyclic heat hydrogen treatment (300 °C), and dehydrogenation in vacuum (550 °C). We present the possibilities of hydrogen treatment for controlling the microstructure layer of titanium alloy and show results for the corrosion resistance of Ti-6Al-4V titanium alloy after hydrogen treatment. Information about the hydrogen effect on titanium alloys, based on selected publications and the authors’ experience, is also presented.