Disclosed herein is a sterically hindered phenolic phosphonate resin compound represented by the following Chemical Formula 1. The present invention also provides a polycarbonate resin composition including the sterically hindered phenolic phosphonate resin compound as a flame retardant. wherein R1 is a C1-C6 alkyl group or a C6-C14 aryl group; each R2 is independently a C1-C6 linear alkyl group or a C3-C6 branched alkyl group; and each n is independently 1-3.