Accountability is present in many types of social relations; for example, the accountability of elected representatives to voters is the key characteristic of representative democracy. We distinguish between two institutional mechanisms of accountability, i.e., opportunity to punish and requirement of a justification, and examine the separate and combined effects of these mechanisms on individual behavior. For this purpose, we designed a decision-making experiment where subjects engage in a three-player trust game with two senders and one responder. We ask whether holding the responder accountable increases senders’ and responders’ contributions in a trust game. When restricting the analysis to the first round, the requirement of justification seems to have a positive impact on senders’ contributions. When the game is played repeatedly, the experience of previous rounds dominates the results and significant treatment effects are no longer seen. We also find that responders tend to justify their choices in terms of reciprocity, which is in line with observed behavior. Moreover, the treatment combining punishment and justification hinders justifications that appeal to pure self-interest.