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An olfactory co-receptor gene AalbOrco was isolated and described from Aedes albopictus using the RACE technique. AalbOrco contained typical structures of seven transmembrane domains and Nin-Cout. Sequence analysis demonstrated that AalbOrco is very similar to Orco orthologs from other dipterans, especially in the C-terminus. AalbOrco was expressed at significantly higher levels in embryos compared with larvae, however, AalbOrco transcripts were found to greatly increase in number from the larval to the pupal stage and were at the highest level at the adult stage. Since AalbOrco is abundantly expressed in adults and is distributed in chemosensory organs such as the antenna, maxillary palps and proboscis suggests that AalbOrco may play an important role in locating hosts. In addition, AalbOrco is also highly expressed in male abdomens as compared to female abdomens, however, no expression was detected in the ovipositor and the copulatory organ. SEM (scanning electron microscopy) and immunolocalization showed that AalbOrco is located in the cell bodies of olfactory sensory neurons (OSNs) under antennal cuticula and the dendrites of neurons in sensilla trichodea. Moreover, fluorescence signals were detected in some neuronal cell bodies and sensilla T2 from the labellum but were scarcely detected in male maxillary palps. The transcription level of AalbOrco in female adults decreased by 55.7% after the larvae continued to ingest exogenous AalbOrco dsRNA expressed bacterially until eclosion. Blood-sucking behavior was impaired by 44.7% compared to the control groups, although pupation and emergence rate were not significantly different between the control and treatment groups. We conclude that AalbOrco has the general characteristics of Orco orthologs and plays an important role in host-locating behavior. AalbOrco performs the olfactory function in antennae as well as in female maxillary palps.