Abstract: An indirect method for determination of DMDMH in cosmetics was proposed. The sample was treated with Nash′s reagent and heated for 20 min in a boiling water bath to derivatize formaldehyde. The supernatant were taken after centrifugation and purified by passing through C18 SPE column. The eluate was used for determination of 5,5-dimethylhydantoin (DMH) and formaldehyde by RP-HPLC with DAD at 210 nm and 410 nm respectively. From the total amount of DMH and HCHO found, amount of DMDMH was calculated. The sample solution was separated by using Kromasil C18 column and acetonitrile-water mixtures with different proportions were used as mobile phase in gradient elution. Ranges of linearity found were between 2.8-280 mg·L-1 (for DMH) and between 0.11-22 mg·L-1 (for HCHO), with detection limits (3S/N) of 0.81 μg·g-1 and 0.033 μg·g-1 respectively. Recovery was tested by addition of standards to 3 substantial cosmetic samples, giving values of recovery in the ranges of 93.4%-107.8% (for DMH) and 97.9%-109.9% (for HCHO) with values of RSD′s (n=5) ranged from 1.7% to 7.3% and 0.8% to 2.3% respectively.