To find the cell cycle inhibitors from the metabolites of Streptomyces flavoretus 18522. METHODS AND RESULTS:Activity-guided isolation was performed on the chloroform extract of the fermentation broth and mycelia of Streptomyces flavoretus 18522 by using ts FT210 cells.Compounds were isolated through various chromatoghraphic methods and elucidated by spectroscopic means.The flow cytometry was used to evaluate the cell cycle inhibiting activity of the fractions and compounds. Six cyclic dipeptides were obtained and identified as cyclo(Ala-Leu)(1),Cyclo(Ile-Ala)(2),cyclo(Ala-Val)(3),Cyclo(Phe-Leu)(4),cyclo(Ala-Pro)(5) and cyclo(Phe-Val)(6).Conclusions Compounds 1-6 are reported as new cell cycle inhibitors for the first time.