Free lysine in a preparation of queen bee's embryo was isolated using cation exchange resin- The Q-aminoand carboxyl group of lysine was complexed with cupric ion and the E-amino group reacted with FDNB(Fluoro-dinitrobenzene). After acid treatment and extraction with ether,the absorbance of the solution at 395nm was determined by spectrophotometry. Variation coefficient of the determination was less than 6% and the recovery of lysine was 95 % ~ 110 %.