Titanium alloys with beta-stabilizing elements have excellent characteristics such as high specific strength, good plastic formability and good corrosion resistance. However, the deformation behaviors of those alloys under biaxial loadings are still not clarified. In this study, uniaxial and biaxial compression tests of binary titanium-niobium alloys (Ti-Nb alloys) of different niobium contents were performed. The influences of niobium contents upon the compressive deformation behavior were then investigated. It was found that the primary plastic deformation mechanism changed with the niobium content and with deformation pattern. As a consequence of that, the different type of anisotropic hardening appeared. The niobium content dependency of constitutive relation of Ti-Nb alloys was then discussed using equivalent stress variation based on an anisotropic yield function and plastic work.