This paper describes the design of a low-cost α+β type Ti-4V-0.6O alloy and the investigation of its microstructure and mechanical properties, with a focus on heat treatability. The β transus (T_β) of the alloy was found to be 1195 K, as determined from the relationship between the heat treatment temperature and the volume fraction of the equiaxed α phase (f_α). The formation of α′ martensite exhibiting an acicular morphology was observed after heat treatments between 1073 and 1273 K. The O content in the equiaxed α and β phases increased with increasing heat treatment temperature while the V content increased with decreasing heat treatment temperature. The alloy demonstrated a higher tensile strength and lower total elongation when heat-treated between 1073 and 1173 K as compared to the as-forged material, because of the formation of α′ martensite. The reduced total elongation was caused by the increase in the hardness difference between the equiaxed α and β (α′ martensite) grains. The tensile strength and total elongation of the Ti-4V-0.6O alloy were comparable to those of the Ti-6Al-4V alloy, which marks the material as a low-cost α+β type Ti alloy candidate.