The sterile insect technique (SIT) is widely used for suppressing or eradicating target pest insect populations. The effectiveness of SIT depends on the ability of released sterile males to mate with and inseminate wild females. Irradiation is the effective manner to sterilize mass-reared insects. The negative impacts of this procedure are not limited to damage on reproductive cells. Gamma-radiation damages the epithelial tissue of midgut, which affects the alimentation in insects. Irradiated males alter their mating behavior over time because of the depression of metabolic activity by sterilization. In this study, we evaluated the male mating performance and sexually compatibility of irradiated male Cylas formicarius elegantulus (Summers) (Coleoptera: Curculionidae) with a 200-Gy dose, as currently used in the SIT program in Okinawa Prefecture, throughout 16 d after irradiation in the laboratory. The mating ability of irradiated males did not differ from that of control males for about a week. However, the mating ability of irradiated male drastically decreased thereafter. We consider that irradiated male C. formicarius elegantulus with a 200-Gy dose had no major effect on male mating behavior approximately for a week after irradiation.