We integrated certainty effect and noninteractive social influence into impulse buying, and explored the relationships between impulse buying tendency and intention in regard to the impacts of certainty effect and social influence. We selected 2 certainty effects (1-phase and 2-phase discounts) and 3 social influences (number, proximity, and strength) that stimulate consumers' impulse buying intention for a unique product. The participants were 416 students at 5 universities in northern Taiwan. Results of structural equation modeling indicated that impulse buying tendency positively influenced impulse buying intention in terms of certainty effects and social influences; there was a positive relationship between certainty effects and social influences in impulse buying intention; the students preferred 2-phase to 1-phase discounts; and, in descending order, the social influences of strength, number, and proximity impacted impulse buying intention. We concluded that marketers can use certainty effects and noninteractive social influences to stimulate consumers' buying intention.