Online retailers employ two strategies of limited-quantity and limited-time to entice consumers’ impulse purchases. However, little research has investigated the effects of these promotion strategies. Drawing on the competitive arousal model and the scarcity model, this paper develops a research model to demonstrate the influences of limited-quantity scarcity (LQS) and limited-time scarcity (LTS) on impulse purchase through the mediating mechanism of perceived arousal. By setting up a new online store on a well-known Chinese e-commerce platform, we conducted a field experiment with 182 participants to test our research model. The results provided strong evidence that both LQS and LTS increased a consumer’s perceived arousal, which then led to impulse purchase. Furthermore, there was an interaction effect between the two types of scarcity strategies on perceived arousal. Finally, although personal impulsiveness positively affected a consumer’s impulse purchase, it did not moderate the influence of perceived arousal on impulse purchase. Our findings provide both theoretical implications and design guidelines on triumphant employment of scarcity promotion strategies.