This work examines the effect of grain size on the mechanical properties of meta-stable β Ti-2Cr-6Sn-45Zr alloys with low Young's modulus. Meta-stable β Ti-Cr-Sn-Zr quaternary alloys with low Young's modulus, which compositions are close to microstructural transition from martensitic microstructure to β phase structure in as-quenched condition after solid solution heat treatment, show stress-induced martensitic transformation. A Ti-2Cr-6Sn-45Zr alloy with meta-stable β phase shows two step yielding phenomenon in tensile stress-strain curves, in which first yield stress indicates the onset stress of stress induced martensitic transformation and second yield stress indicates the onset of slip deformation. The grain size of this alloy influenced its mechanical properties, that is, first yield stress decreased and the second yield stress increased as the grain size of the alloy diminished. Young's modulus was not influenced greatly.