There are three kinds of secondary metabolites in Monascus fermentable extract: red pigments, monacolin K and citrinin. Red pigments are natural food colorants widely used in food industry. Monacolin K acts as lovastatin to decrease blood cholesterol and promot blood circulation. Citrinin is a nephrotoxic activity in mammals. Although some citrinin-nonproducing mutants of Monascus have been constructed by induced mutation, but the mutants easily generate revertants. In order to determine the exact location of the mutation and explain the citrinin pathway, essential method is to disrupt the gene for citrinin biosynthesis. In Monascus species, transformation is relatively easily achieved through protoplasts (1). But gene disruption has been difficult to achieve. Only a research of pksCT- insert-disrupted has been reported in Monascus purpureu, but Revertants generated in disruptant restored citrinin production (2). Genomic DNA were isolated from three high producers of red pigments and citrinin strains (M.purpureus 3.4451, M.purpureus 3.4453, M. aurantiacus Li 3.4384 ) and one citrinin-nonproducing and red pigments-lowproducing strain (M. rubber van Tieghem IFFI 5007). Two portions in both ends of pksCT gene (accession no. AB167465 in GenBank) were amplified by PCR, using genomic DNA as templet. A pksCT -replace -disrupted vector constructed to replace pksCT with a hygromycin resistance gene was transformed into Monascus through electroporation. Transformants were subcultured on selection plates (contain 50 mg L ^-1hygromycin B). The citrinin levels in fermentation of pksCT disruptants were analysed by HPLC.Two portions of pksCT were gained from M.purpureus 3.4451, M.purpureus 3.4453, and M. aurantiacus Li 3.438，but M. rubber van Tieghem IFFI 5007. Results showed that pksCT disruptants produces have little or no citrinin, and there is no revertant generated in pksCT disruptants by successive cultivate.