Citizen science is a form of crowdsourcing service that recruits general public on scientific collaboration and co-creation. Drawing upon the job characteristic theory and self-determination theory, this paper investigated the influences of five task characteristics, including importance, interdependence, complexity, specialization, and feedback on individuals’ psychological needs, which in turn affected users’ participation intentions. We are also interested in how gamification design moderates the impacts of task characteristics on psychological needs. We conducted an online experiment to validate our research model. Our research findings showed that three psychological needs have positive impacts on participation intentions. Importance of task influences relatedness positively; feedback has a positive impact on competence; specialization and complexity affect competence negatively. Particularly, our findings confirmed the moderating effects of game elements. Research and practical implications for citizen science task design are also discussed.