["Journal of Consumer Behaviour, EarlyView. ", "\nABSTRACT\nAlthough firms widely assume that surprise rewards enhance customer loyalty, empirical evidence shows that the effects of surprise rewards are inconsistent and may even backfire under certain conditions. This raises a critical question: under what circumstances do surprise rewards effectively foster customer loyalty? As more firms adopt surprise marketing, addressing this issue has become increasingly urgent. Building on attribution theory, this study conceptualizes surprise rewards as events that activate consumers' causal reasoning. When consumers experience surprise, they assess the motives behind the firm's behavior, and loyalty increases when these rewards are attributed to customer‐serving motives. This process is further shaped by two boundary conditions, namely explanatory information and consumer cynicism. Across three online experiments, we identify customer‐serving attribution as the central psychological mechanism linking surprise rewards to loyalty. Providing explanatory information strengthens customer‐serving attributions, which in turn enhance customer loyalty. This effect is especially pronounced among consumers with high levels of cynicism. Overall, this research identifies the cognitive mechanism and boundary conditions through which surprise rewards foster customer loyalty, offering a novel theoretical perspective on surprise marketing and actionable insights for designing effective reward strategies.\n"]