A sintered alloy for a valve seat may be manufactured using a method including: mixing MnS with an alloy powder for a valve seat including C at 0.8-1.2 wt %, Ni at 2.0-4.5 wt %, Cr at 3.0-5.0 wt %, Mo at 16.0-20.0 wt %, Co at 9.0-13.0 wt %, V at 0.05-0.15 wt %, S at 0.2-0.8 wt %, Fe, and additional inevitable impurities; making a first shape by forming the mixed materials; pre-sintering the first formed shape; making a secondary shape by re-pressing the first pre-sintered shape; main-sintering the secondary shape; and tempering the main-sintered secondary shape.