Phentermine (PT) and phenmetrazine (PM) have been widely used as anti-obesity drugs. These drugs should be used with caution due to its close relation to amphetamine in its structure and toxicity. PT and PM, amphetamine-type anorectics, have recently been considered as alternatives for methamphetamine abuse in Korea. In addition, the misuse and abuse of PT and PM obtained by illegal sources such as the internet become a serious social problem. In the present study, a simultaneous detection and quantification method for determining PT and PM in human urine was developed and validated according to the international guidelines. The urine samples were screened using a fluorescence polarization immunooassay and analyzed by gas chromatography mass spectrometry (GC-MS) after extraction using automatic solid phase extraction (SPE) with a mixed-mode cation exchange cartridge and derivatization with pentafluoropropionic anhydride (PFPA). The validation results for selectivity, linearity, limits of detection (LOD) and quantification (LOQ), intra- and inter-assay precision and accuracy and recovery were satisfactory. The validated method was successfully applied to authentic urine samples collected from 38 drug abuse suspects. PT and/or PM were identified with or without methamphetamine in urine samples. Abuse of PT and PM have increased continuously in Korea, therefore, closer supervision of the inappropriate use of anoretics is necessary.