Electron beam (EB) welding of Ti-24Al-17Nb-0.5Mo (at.%) alloy and the effects of postweld heat treatments (PWHT) were studied. Through optimizing the welding parameters, defect-free welding joint was obtained. For the as-welded joint, the fusion zone (FZ) consisted of predominant β and occasional α2 within β grains. Microhardness of FZ was higher than that of the base metal (BM) and that of the heat affected zone (HAZ) was between that of BM and FZ. PWHTs greatly modified the microstructures and mechanical properties of the weld zone. PWHTs at both 820oC and 900oC yielded fine acicular laths in FZ leading to severe brittleness of the weld. Appropriate microstructures and phase combination were obtained by PWHT at 1000oC for 2 h, and room-temperature tensile strength reached the value of the base metal after the same thermal cycle.