This paper describes an assay method to determine free formaldehyde in cosmetics using High Performance Liquid Chromatography (HPLC), with a pre-column derivation with 2,4 dinitrophenylhydrazine. The derivatives were analyzed using a RP8 column with 45% acetonitrile solution as mobile phase and detected at the wavelength of 345 nm. The detection limit of derived formaldehyde in this HPLC system was 0.2 ppm. Compared with the amounts of formaldehyde analyzed from the 0.2% formaldehyde donors, the results obtained by acetylacetone method were 1.62~17.35 times higher than that of HPLC method. One hundred cosmetic products purchased during 1995-1996 were investigated. None of those products was labeled formaldehyde. The results showed that 53% of the samples were formaldehyde positive. The amounts of total free formaldehyde were between 3~165 ppm. All of them were less than 1000 ppm.