As emerging approaches, IT-based applications designed for encouraging pro-environmental behaviors have shown great potential. By focusing on Ant Forest, this study attempts to explore the embedded gamification design to identify key elements that lead to users’ long-term game participation which eventually fosters pro-environmental behaviors. First, a focus group interview was conducted to identify twenty-one gamification design elements in four modules: task design, social interaction, feedback, and reward. Furthermore, this study employed the Two-Dimensional Kano Model and better–worse analysis to classify and prioritize the gamification design elements that impact users’ attitudes toward Ant Forest. Five Attractive elements, five One-Dimensional elements, four Must-Be elements, and seven Indifferent elements were identified in Ant Forest from 207 questionnaires. The results emphasize the significant impact of gamification design elements that are highly correlated with environmental sustainability (i.e., green context, pro-environmental behaviors, plant a tree) in Ant Forest. In addition, users who are rewarded by both virtual medals and official certificates demonstrate higher satisfaction, whereas elements associated with social interaction and competition show trivial importance. This study has profound theoretical implications as an interdisciplinary study, and yields helpful insights for practice to improve Ant Forest design, promote Ant Forest usage and finally fuel pro-environmental behaviors.