Abstract: Objective The Musca domestica larvae secretion was extracted from the leaching liquor of fed remnant and larvae.The effect was studied on the development of ascaris suum eggs after simple purification.Methods The fed remnant and 3 instar larvae were soaked in distilled water for 4 hours,then the leaching liquor was isolated with salting out by solid ammonium sulfate or dialyzing.The secretion was prepared as culture liquid of ascaris suum eggs.The developmental ration of the egg was observed and compared with the control group which cultirated in same condition without the musca domestica larvae secretion.Results The 0~30%、30%~50% ammonium sulfate pellets and sulfate supernatant of the leaching liquor of fed remnant and larvae did not showed influence to the development of ascaris suum egg,while the 50%~80% sulfate pellets,dialyzed liquid could hinder the growth of egg obviously.Conclusion The leaching liquor of fed remnant and larvae can hinder the growth of ascaris suum egg.The major substance were the 50%~80% sulfate pellets,the molecular weight of which was no more than 14KD.