The full‐length cDNA of the gene SlituOR18, encoding a candidate olfactory receptor in the antennae of the tobacco cutworm, Spodoptera litura (Fabricius) (Lepidoptera Noctuidae), was identified through homology cloning strategies using RACE (rapid amplification of cDNA ends) and PCR (polymerase chain reaction). The protein of SlituOR18 shared >80% sequence identity and the same seven transmembrane domains with other olfactory receptor 18 (OR18) proteins sequenced from noctuid moths. SlituOR18 also had a similar structure to SlituORco, encoding the olfactory co‐receptor in S. litura. The sequence between transmembrane segments IV and V was longer than other sequences between transmembrane segments, and the N‐terminus was intracytoplasmic. Analysis by qRT‐PCR showed SlituOR18 was predominantly expressed in adult moths and there was higher expression in female antennae than in male antennae. Weak expression of SlituOR18 was observed in eggs and no expression was observed in the antennae of fourth instars and 5‐day‐old pupae. In situ hybridization experiments revealed that expression of these receptor types was clearly restricted to the bases of trichodea‐type olfactory sensilla (sensillum trichodeum), that are known to contain neurons sensitive to food odor or pheromones. Our data demonstrated that both SlituORco and SlituOR18 showed diurnal changes in their relative expression level. Expression of SlituOR18 varied among geographic populations of S. litura that had been trapped in the field using synthetic pheromone lures. The mRNA expression level of SlituOR18 was similar among S. litura populations from Sichuan, Guangxi, and Hunan, and higher than in populations from Shanghai and Ningbo. We suggest that OR18 could play a critical role in olfaction in noctuid moths and is a potential target for novel pest management strategies in the future.