OBJECTIVE To improve the synthetic process of selamectin.METHODS As the starting material,doramectin was firstly oxidated by manganese dioxide and then the key intermediate 25-cyclohexyl-25-de(l-methypropyl)-5-demethoxy-5-hydroxyimino-avermectin Bla monosaccharide was obtained via deglycosidation and oximation.Selamectin was prepared by hydrogenation after recrystallization with acetonitrile and water.RESULTS The structures of intermediates and product were confirmed by 1H-NMR,13C-NMR and HPLC-HRMS,the total yield was 53.2%and the purity of the product was 97.1%.CONCLUSION This synthetic process is charactered by simplified step,simple operation,high yield and lower cost,which exhibits the potential to be applied for industrial production.