Accurate diffusivities are essential for the design and production of biomedical alloys with excellent properties. In the present work, ternary and quaternary interdiffusion behaviors in Ti-rich Ti-Nb-Cr, Ti-Zr-Cr and Ti-Nb-Zr-Cr systems at 1273 K were experimentally investigated via the diffusioncouple technique. Ternary interdiffusivities of bcc Ti-Nb-Cr alloys were then determined using the Matano-Kirkaldy method. Subsequently, on the basis of the presently obtained interdiffusivities together with the diffusivity and mobility parameters of Ti-Nb-Zr-Cr sub-binary and sub-ternary systems and the thermodynamic descriptions for bcc Ti-Nb-Zr-Cr system, the atomic mobilities of Ti,Nb, Zr and Cr in bcc Ti-Nb-Zr-Cr alloys were assessed by means of CALPHAD (CALculation of PHAse Diagrams) method. Moreover, the comprehensive comparisons between the experimental diffusion properties of bcc Ti-Nb-Cr, Ti-Zr-Cr and Ti-Nb-Zr-Cr systems (i.e., interdiffusivities, composition profiles, interdiffusion fluxes and diffusion paths) and the calculated/model-predicted data due to the present atomic mobilities were conducted in order to verify the reliability of the mobilities. The present atomic mobilities for bcc Ti-Nb-Zr-Cr system can provide the accurate ternary and quaternary interdiffusivity matrices over a wide composition range.