Abstract: The compositions of nystatin from different sources including International standard, Chinese working standard and samples of nystatin from manufacturers both inside and outside China were compared by using HPLC.Eight to ten peaks were obtained. The peak areas were processed with Sigma 10 Chromatography Data Station. From the chromatograms, the main components as well as their peak areas of all Chinese samples including Chinese working standard for nystatin differed from those obtained from some foreign countries.The main components of Chinese working standard for nystatin were peak 9 and peak 13 with peak areas of 55% and 20.1% of the total area respectively, while the main component of International standard for nystatin was peak 11 with peak area of 81% of the total area.The nystatin made in China was obtained from Actinomyces noursei isolated from soil in Guangdong. The nystatin obtained from foreign countries was from Streptomyces noursei. This might account for the difference in the HPLC results.Samples were subject to careful purification with HPLC using a semi-preparative column. The eluents collected were lyophilized and the purified samples from Chinese working standard for nystatin were assayed according to current Chinese Pharmacopoeia. The potency found with the purified sample from peak 13 (nystatin C₂) was 10,800 u/mg (±4.4%), whereas purified sample from peak 9 (nystatin C₁) gaves potency estimated much lower than the parent material.HPLC conditions:For analytical purpose: Column ODS-HC SIL-X-1, 0.26×25 cm; mobile phase MeOH—H₂O (68:32)) flow rate 1.3 ml/min; UV detector at 304 nmFor preparative purpose: Column 10 μm Nucleosil ODS, 0.7×25 cm; flow rate 5 ml/min; the rest of the conditions was same as above.