To study effects of Cu and Sn addition on the sintering behavior of SUS304L stainless steel powders and mechanical properties of their sintered compacts, 4 mass Cu and 1 mass Sn pre alloyed SUS304L stainless steel powder and 2 mass Cu mixed this powder were sintered at 1323～1523 K in vacuum after compacted at the pressure of 490 MPa. In addition to density measurement, micro structural observation and tensile test for each sintered compacts, differential scanning calorimetry and thermomechanical analysis for each powder were conducted.As a result, alloying elements of Cu and Sn in the powders were considered to generate liquid phase around 1150 K. Moreover, alloying elements of Ni in the powders was considered to react with Cu Sn phase during sintering and resulted to form Cu Sn Ni liquid phase near 1400 K. These liquid phase led to the densification of the sintered compacts. The tensile strength of sintered compact of all powders sintered at 1523 K showed superior or comparable to the JIS value of bulk SUS304L.