Abstract: A new causative agent attracts us in present control of the myiasis of Przewalski′s horse. The species, which is attributed to Gasterophilus, Gasterophilidae, Diptera according to the collected larva specimen, has been unrecorded in national literatures by now. Features of the 3rd instar larvae were as follows: fully-grown larvae (maggots) are 14-17 mm long (double of the width) and have green, tough skin; the body is spindly and blunt at the back end; the front part of each body segment (from the 3rd thoracic segment to the 6th abdominal segment) is ringed with single line of strong, yellow, longitudinal-narrow spines. The line of spines at the backside become incomplete since the 4th abdominal segment, and there is no spine at the backside of the 7th abdominal segment.