Abstract: The trimethylsilylation of testosterone and epitestosterone was discussed in detail inthis reprot. Both derivative conditions under which testosterone and epi-testosrone were prepared intoTMS-derivatives in the presence of mercaptoethanol as an antioxidizing agent and method for the analy-sis of the ratio of testosterone to epi-testosterone in urine, based on GC--MS, had been established.The conditions of detection were: carrier gas was helium, derivatives were separated with SE-54 fusedsilica capillary column, using temperature program and detected by using mutiple ion detection mode inwhich the ion of m/z 432 was the monitoring ion. The method is rapid, sensitive and specific. For theratio of testosterone to epi-testosterone(testosterone:20 ng/μl), there is a linearity between ratio 1:1and 10:1(r=0.998), the limit of detection for testosterone and epi-testosterone is 1 ng, and the mi-nimum concentration of detection in urine is 8 ng/ml.