This article investigates if and how negotiators' self-efficacy beliefs affect their use of deception in negotiation. Specifically, we propose that self-efficacy can be interpreted as a threat to self-concept, which encourages individuals to temporarily bypass self-regulatory obstacles by morally disengaging their cognitive moral filters, thereby enabling them to use deception in negotiation. We test our hypotheses in three independent experimental studies involving an interactive negotiation simulation, totalizing 460 participants. We find that negotiators with low self-efficacy regarding their negotiation abilities are (...) more likely to use deception than those with high self-efficacy beliefs. Furthermore, we find that moral disengagement mediates the effects of self-efficacy on deception. Our findings suggest that self-efficacy plays a key role in shaping negotiators' ethical behaviors and we identify the psychological mechanism underlying this relationship. (shrink)