Sintering behaviors of two types of powder compact, i.e., Ti/Al and TiH2/Al, under vacuum were studied using in situ neutron diffraction, in situ thermal dilatometric measurement, and ex situ neutron radiography. Their densification, microstructure, hydrogen concentration, and phase transformation features were compared. The results indicate that the predominant phase identified in the samples sintered from both compacts is γ-TiAl phase with minor Ti3Al phase. Dehydrogenation of TiH2 plays a decisive role in the sintering behavior and the resultant microstructure. In comparison with the Ti/Al compact, dehydrogenation occurring in the TiH2/Al compact leads to a higher level of densification and faster sintering kinetics.