The effect of cooking peanut kernels before grinding on the hexanal content of peanut milk was investigated. Hexanal which is thought to be one of the major compounds contributing to the beany flavor of peanut milk, was quantified using a simplified headspace gas chromatographic method. Four cooking times (0, 10, 20 and 30 min) were evaluated. The concentration of hexanal in peanut milk was one-third by cooking peanut kernels for 10 min or longer. Protein content of peanut milk gradually decreased by heat treatments.