Parasitoid populations having optimum male: female ratios are generally released in the field during the cocoon stage for an effective bio-control program. Due to the distinctive habit of forming a cocoon within the shrunken larval body of the host, cocoons of both sexes of the icheneumonid wasp, Hyposoter ebeninus, displayed morphological similarities. Therefore, male and female cocoons cannot be differentiated based on normal morphological parameters. In this report, we tested several combinations of morphological parameters and size indices and developed a simple technique for separation of sexes at the cocoon stage of this wasp. Among ten possible parameters tested, the weight of the cocoon was found to be the most appropriate and reliable parameter for sex separation with a 100% success rate. Since this technique involves only one parameter, it is simple, robust and requires minimum technical skill. This technique would be very useful for research workers, commercial biological control laboratories and other related agencies working on H. ebeninus.