Momordica seed proteins was prepared and investigated for the cytotoxic effect against two breast cancer cell lines, MCF-7 and T47D.The frozen ripe seeds of Momordica charantia L. were obtain the contact in farmer from Supanburi province. The seed proteins were extracted with normal saline precipitated with percentages of ammonium sulfate solution; they were 0-30%, 30-60%, 60-90% and 90%. The protein fraction was performed. The extraction and precipitation of the seed proteins were concluded hygienically at 4ºC.