As environmental sensitivity among modern consumers continues to escalate, corporations are increasingly fortifying their ESG and CSR initiatives. Consequently, designing effective messaging strategies to persuade consumers through green advertising has become a critical imperative. This study investigates the interaction effects between claim types (substantive vs. associative) and fear appeal types (physical vs. social) in green advertising on advertising attitudes and information-sharing intentions. Fear appeal, characterized by emphasizing the potential losses and hazards of failing to comply with recommended messages, holds significant strategic value in the context of pro-environmental behavior, which often necessitates personal cost, inconvenience, or effort. Grounded in a 2x2 experimental design, this study conducted an experiment with 160 university students interested in environmental issues. The empirical results reveal a significant interaction between the type of claim and the type of fear appeal. Specifically, substantive claims yielded more favorable advertising attitudes and higher information-sharing intentions when paired with physical fear appeals, whereas associative claims were more effective when combined with social fear appeals. Furthermore, the interaction effect on information-sharing intention was found to be mediated by advertising attitudes. These findings highlight the critical importance of "message fit" between claim and appeal types in green advertising design and provide strategic implications for the effective utilization of fear appeals in sustainable marketing.