The effects of hydrogen additions (hydrogen content, C(H) = 0-0-9 Wt.%) on microstructural characteristics and precipitation behavior have been investigated in beta-Ti40 titanium alloy of the general composition Ti-25V-15Cr-0.2Si (wt.%). The microstructures were studied using optical microscopy (OM), X-ray diffractometry (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The results showed that hydrogen addition had a noticeable influence on microstructure of beta-Ti alloy. Hydrogen addition decreased the solid solution solubility of Si element leading to the precipitation of Ti(5)Si(3) phase. Effect of hydrogen content on the microstructural model was established. (C) 2009 Published by Elsevier Ltd on behalf of International Association for Hydrogen Energy.