As one of the designer drugs, of which the abuse has become a serious social problem worldwide, m-trifluoromethylphen ylpiperazine (TFMPP) acting as a psychoactive drug related both to the amphetamine type stimulants (ATS) and mescaline-like hallucinogens having been controlled by Narcotics and Psychotropics Control Law of Vietnam since April 10th 2011, was quantitatively determined (in tablets) by capillary GC-FID with docosan as internal standard. Experimentally, the method showed desirable accuracy, satisfatory precision and sufficient selectivity. Analysis of eleven tablet samples from eleven cases revealed the content of 67.8 - 261.2 mg of TFMPP per tablet.