Bed bugs (Cimex spp.) (Hemiptera: Cimicidae) are obligatory blood-sucking insects. Research on their behavioral response to host-derived olfactory cues will be helpful for designing more effective management tools. However, previous studies mainly focused on Cimex lectularius L., while the related studies on Cimex hemipterus (F.) have been rarely reported. In this study, we evaluated the behavioral responses of C. hemipterus to one of the crucial host-derived cues – carbon dioxide (CO₂), at various concentrations. Pitfall traps baited with CO₂ captured significantly more C. hemipterus (72%) than unbaited ones (28%). In the Y-tube test, bed bugs' exploratory activity (response rate) gradually decreased (from 70 to 27%) as the CO₂ concentration increased (from 0.9 to 14.5%); and bed bugs exhibited a significant attraction to CO₂ when the tested CO₂ concentrations were between 0.9 and 7.3%. Cimex hemipterus were no longer attracted to CO₂ after their antennae or mouthparts or both antennae and mouthparts were removed. In conclusion, C. hemipterus are attracted to CO₂, and both antennae and mouthparts are important for CO₂ perception.