In this study, biaxial compression tests along proportional and non-proportional strain paths were performed on binary titanium-niobium alloys (Ti-Nb alloys) of different niobium contents, in order to clarify the deformation behaviors of those alloys under biaxial loadings. The influences of strain path and niobium content upon the compressive deformation behavior were then investigated. It was found that there were differences on stress-strain relations of Ti-Nb alloys owing to the different primary plastic deformation mechanisms. The clear influence of strain path change on the compressive behavior of Ti-35Nb alloy was observed, probably because of the activation of new twin systems after the path change.