This study investigates the effect of culture and salespersons’ retail service quality on impulse buying and provides evidence that service quality moderates the effect of culture on impulse buying. The experiment uses a 2 (culture of participants: Singaporean versus American) by 2 (retail service quality: poor versus good) between-subjects factorial design with 102 Singaporean and 88 American working adults recruited from companies in Singapore. It finds that for both cultures, good service leads to higher impulse buying than does poor service. The significant interaction between culture and service quality on impulse buying indicates that when service is good, Singaporeans show higher impulse buying than do Americans. In contrast, when service is poor, Singaporeans reveal lower impulse buying than do Americans. The implication is that multinational companies should invest in creating and assuring good service quality when they do business in collectivist cultures but might give relatively higher weight to other kinds of competitive advantages when they do business in individualist cultures.