Abstract: Olfaction plays a vital role in host-seeking, enemy-defending, mating and immigration in natural enemies. Olfactory receptors are an important class of functional proteins in insect olfactory system. In this study, a sequence fragment of olfactory receptor gene MmedOr2 in Microplitis mediator was identified from the antenna cDNA library, and the full-length sequence of this gene was obtained by using rapid amplification of cDNA ends (RACE). Further, expression profiles of this gene in different tissues along the developmental stages, as well as before and after mating was analyzed using real-time quantitative PCR. It was found that the receptor gene was specifically expressed in antenna, and expression level was significantly higher in female than in male. In female, MmedOr2 expression reached the highest level on the 3rd day after emergence while the highest expression in male appeared on the 4th day after emergence. After peak expression, MmedOr2 expression level declined gradually in both male and female adults. In addition, expression level of MmedOr2 in female adults was notably decreased after mating. According to above findings, we speculate that MmedOr2 may be a sex pheromone receptor and plays an important role in mate-searching.