Objective:To establish a simple and effective washing procedure for both used and purchased mineral oil,that can be used for embryo culture.Methods:A complete test system has been used for this purpose.There are 3 steps in our new washing proto-col.First,the oil was mixed with 95% ethanol at 1:1,the bottle being shaken by hand for 10 minutes,then sepa-rated.Second,the oil was heated to boiling point with 0.31 mol/L NaCl for 30 minutes.Third,anhydrous Na:SO4 was put into the oil for further treatment.1-cell stage embryos of a KM strain mouse have been collected surgically and cultured.Cleavage and blastocyst stage development were recorded and some embryos were transferred into re-cipients.Results:The results show that recycled oil can promote the development from 2-cell to blastocyst stage(23.3%)when compared with that of control(16.9%).Offspring have been obtained at 44 %(7/16),16 %(3/19)from washed recycled oil and control oil respectively.Conclusion:This washing procedure is safe and effective for the used treatment and for other sources of mineral oil used for embryo culture.