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Trichogramma japonicumAshmead (Hymenoptera: Trichogrammatidae) is a biological control agent that parasitizes the eggs of many lepidopteran insects. The control efficiency is closely related to the ability of the parasitoid to use chemical volatiles in searching for hosts, and the odorant binding proteins (OBPs) may serve as a first step in the perception of these chemical cues. Understanding the ability of Trichogrammato detect relevant host odorant cues might help to design better strategies to control target lepidopteran insect pests. In the present study, we assembled the transcriptome of T. japonicumusing Illumina sequencing technology and identified 15 putative OBP genes. All the OBP genes have complete open reading frames and contain six conserved cysteines. In addition, sex-biased expression was found in eight OBP genes by using quantitative real-time PCR, which suggested different functions of these genes. Phylogenetic analyses revealed that Hymenoptera OBP genes were divided into Classic, Minus-C, and Double Minus-C subfamilies. All the identified OBP genes of T. japonicumbelong to the Classic subfamily. These results provide an important foundation for a better understanding of the complex chemoreception system of T. japonicum.