The physiologically active subatance produced by monascus sp. has been researched widely. at the same time ,most of monascus sp. were proved to produce citrinin, which is a mycotoxin. Citrinin in HongQu(monascus sp.)has affected the HongQu export of our country.The property of citrinin produced by monascus sp. is introduced in this paper including Occurrence, biosynthesis, detection methods and some measures to avoid its production.