In this study, effect of GTAW process on the structure, corrosion behavior and mechanical properties of Ti6Al4V alloy weldment was investigated and the corrosion behavior and mechanical property were improved using of preweld and postweld heat treatments. For this purpose, thin sheets of Ti6Al4V alloy GTA welded where welding heat input was 350 J/mm. In order to study the effects of heat treatment on the weldment structure, corrosion behavior and mechanical properties, a combination of stress relieving, solution treatment and aging on thin sheets of this alloy was done. The stress relieving and aging treatments were carried out at 600°C and 540° C, respectively, for 1 h, followed by air cooling. The solution treatment was performed at 950°C for half an hour followed by water quenching. Structural characteristics and mechanical properties of weldment were studied by optical and scanning electron microscopy (SEM), X ray diffraction, tension and hardness test. The electrochemical behavior of weldment was also studied in Ringer’s solution using open circuit potential-time measurements and tafel polarization. Structural investigations reveal presence of coarse primary ? grains plus discontinuous ? phase along the ? grain boundaries in the fusion zone (FZ). Furthermore there was no sharp interface between FZ and heat affected zone (HAZ). This case was attributed to epitaxial growth of ? grains in FZ from coarsened ? grains of near heat affected zone (NHAZ). This structure caused decreasing of corrosion resistance and elongation of weldment. The results of investigations showed that size and shape of columnar ? grains do not tailor by any heat treatment below ? transformation temperature (T ? ). Heat treatment used to improvement of corrosion behavior. The results of corrosion tests showed that solution treatment and aging after welding improve corrosion behavior of weldment and no preferential attack was not observed between base metal (BM), FZ and HAZ. This phenomenon was attributed to formation of ? from martensite and ? from metastable ? and also coarsening of ? plates during heat treatment. Furthermore low temperature postweld heat treatments, like stress relieving, and also preweld heat treatments did not have any appreciable effect in improving the corrosion behavior of weldment. The results showed that weld ductility of as-welded sample 100% improved and hardness of diffrent zones was uniformed by subjecting it to a solutionizing and aging treatment.