Abstract UCN-01 is a naturally derived anticancer agent isolated in the culture broth of actinomyces streptomyces. We have developed a sensitive high-performance liquid chromatographic method for the determination of UCN-01 in human plasma. UCN-01 was isolated from human plasma after intravenous administration, by using 100% ice-cold acetonitrile liquid–liquid phase extraction. Liquid chromatographic separation was achieved by isocratic elution on a phenyl analytical column. The mobile phase consisted of acetonitrile–0.5 M ammonium acetate (45:55) with 0.2% triethylamine added as a modifier. The UCN-01 peak was identified from other peaks using fluorescence excitation energy and emission energy wavelengths of 310 and 410 nm, respectively. Retention time for UCN-01 was 4.2±0.5 min. The UCN-01 peak was baseline resolved, with nearest peak at 2.6 min distance. No interfering peaks were observed at the retention time of UCN-01. Peak area amounts from extracted samples were proportional over the dynamic concentration range used: 0.2 to 30 μg/ml. Mean recoveries of UCN-01 at concentrations of 0.5 and 25 μg/ml were 89 and 90.2%, respectively. Relative standard deviations for UCN-01 calibration standards ranged from 1.89 to 2.31%, with relative errors ranging from 0.3 to 11.6%. Assay precision for UCN-01 based on quality control samples of 0.50 μg/ml was ±4.86% with an accuracy of ±5.7%. For drug extracted from plasma the lowest limit of detection was 0.1 μg/ml, with the lowest limit of quantitation being 0.2 μg/ml. This method is suitable for routine analysis of UCN-01 in human plasma at concentration from 0.2 to 30 μg/ml.