The yellow mealworm beetle, Tenebrio molitor (Coleoptera: Tenebrionidae), is a common insect pest that damages stored grain. The insect olfactory co-receptor (Orco) is a transmembrane protein localized on the surface of the dendrites of olfactory sensory neurons and plays an essential role in the olfactory perception. In this study, an Orco ortholog (named as Tmol\Orco) in T. molitor was characterized. The deduced amino acid sequence of Tmol\Orco shared significant high identities with Orcos in other insect species from distinct Orders. Reverse transcription quantitative PCR (RT-qPCR) analysis showed that Tmol\Orco was predominantly expressed in the antennae of both male and female adults, and the difference between male antennae and female antennae was not significant. Double-stranded RNA (dsRNA) directly against the Tmol\Orco mRNA was synthesized and injected into the T. molitor male adults, RT-qPCR results demonstrated that the transcription level of Tmol\Orco was significantly reduced at 6d after the injection. The mate-seeking behavior of Tmol\Orco-silenced beetles was significantly inhibited. Compare to the control individuals, the percentage of Tmol\Orco-silenced beetles successfully find mates was significantly decreased and the average time they spent for searching were significantly increased. These results provided first direct evidence that suppression of Tmol\Orco transcription contributes to the decline in mate recognition of T. molitor.