The parasitoids of Cotton Bollworm Microplitis mediator (Hymenoptera: Braconidae) find their hosts through the odor released by stressed plants. In this study, preliminary characterization and isolation of cDNAs from male M. mediator antennal libraries identified 8 putative odorant-binding proteins (OBPs). Real-time polymerase chain reaction method was used to study the expression pattern of these isolated genes. Their gene expression profiles under a wide range of conditions indicated that only 4 OBP genes in M. mediator were antenna specific. The remaining 4 genes are either expressed ubiquitously or strictly regulated in specialized tissues or during different developmental stages. Some OBP genes were gender specific. These findings support that OBPs play dynamic roles during development of M. mediator and are likely to be involved in broader physiological functions.