Although follower helping behavior has been widely studied, knowledge about how such behavior promotes negative leader behavior is still limited. Drawing upon social cognitive theory, we develop and test a theoretical model of how and when follower helping behavior leads to leader exploitation. Through an experiment and a multi-wave field study, we found that follower helping behavior was positively related to leader perceptions of follower's willingness to self-sacrifice, which increased the possibility of leader exploitation. Furthermore, we found that leader bottom-line mentality moderated the indirect effect between follower helping behavior and leader exploitation; leader with high bottom-line mentality was more likely to exploit follower after perceiving follower as willing to self-sacrifice. Taken together, our findings present a novel framework for understanding how follower helping behavior can give rise to negative leader behavior, thereby inspiring the ongoing interest of scholars and practitioners in helping behavior research and leadership research.