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A simple and sensitive high-performance liquid chromatographic (HPLC) method with fluorescence detection and mass spectrometric identification has been developed for analysis of 30 long-chain and short-chain free fatty acids (FFAs). The fatty acids were derivatized to their esters with 1-[2-(<i>p</i>-toluenesulfonate)ethyl]-2-phenylimidazole-[4,5-<i>f</i>]-9,10-phenanthrene (TSPP) in <i>N</i>,<i>N</i>-dimethylformamide (DMF) at 90 °C with anhydrous K<sub>2</sub>CO<sub>3</sub> as catalyst. A mixture of C<sub>1</sub>-C<sub>30</sub> fatty acids was completely separated within 60 min by gradient elution on a reversed-phase C<sub>8</sub> column. Qualitative identification of the acids was performed by atmospheric-pressure chemical ionization mass spectrometry (APCI-MS) in positive-ion mode. The fluorescence excitation and emission wavelengths were 260 and 380 nm, respectively. Quantitative determination of the 30 acids in two Tibetan medicines <i>Gentiana straminea</i> and <i>G. dahurica</i> was performed. The results indicated that the medicines contained many FFAs. Linear correlation coefficients for the FFA derivatives were >0.9991. Relative standard deviations (RSDs, <i>n</i> = 6) for the fatty acid derivatives were <3%. Detection limits (at a signal-to-noise ratio of 3:1) were 3.1-38 fmol. When the fatty acid derivatives were determined in the two real samples results were satisfactory and the sensitivity and reproducibility of the method were good.