The surface-reacted layer of titanium castings greatly affects their mechanical properties. This study analyzed the interfacial zone of Ti-20%Zr-5%Cr alloy castings obtained from phosphate bonded investment and examined the relationship between the surface-reacted layer and hardness. The Vickers hardness of cast disks were tested at 20$mu m$ intervals from the surface to 120$mu m$ in depth. The cross-section was observed metallurgically, and line profile of the reacted layer was conducted under the EDX. The surface-reacted layer of Ti-20%Zr-5%Cr alloy is showed a similar tendency to Ti-6%Al-4%V alloy in thickness, and also Si diffusion in multiple reacted layer of Ti-20%Zr-5%Cr alloy is less than cp Ti and similar to Ti-6%Al-4%V alloy. The Vickers hardness in the surface layer was greater than in the inner part, and the Vickers hardness of Ti-20%Zr-5%Cr alloy ranged 650 to 390 and cp Ti ranged 810 to 160, Ti-6%Al-4%V alloy ranged 710 to 530 respectively.