Abstract: Long chain dicarboxylic acids reacted with Cu2+ in methanol solution of CuSO4 to form a precipitate. After centrifugation, absorbance of the supernatant was determined at 820 nm. Based on this fact, a photometric method for indirect determination of long chain dicarboxylic acids was proposed. Linear relationship between values of absorbance and mass concentration of long chain dicarboxylic acids was kept in the range of 5-40 g·L-1, with detection limit (3s/k) of 0.011 g·L-1. Values of recovery were found in the range of 104%-105%, and RSD′s (n=5) were less than 0.6%.