For SCS-6 SiCf/RBSC composites fabricated by the Si melt infiltration in vacuum atmosphere it was found that the coating layer on SiC fiber direcly affected the interfacial reaction between fiber and matrix as well as the mechanical properties of composites. SiC/C double coating layer on SiC fiber was found to be most effective to improve the fracture toughness of SiCf/RBSC composites byminimizing the interfacial reaction between fiber and molten Si,. The maximum fracture strength and toughness of 25vol% SiCf/RBSC composites fabricated in vacuum was 540 MPa and 12.4MPa$.$m1/2 respectively. However for the composites fabricated by the Sil melt infigtration in Ar atmosphere it was found that any type of coating layer on SiC fiber could not reacted the interfacial reaction between fiber and molten Si due to the oxidation of the applied coating layer