This study investigates the impact of the tax system's accountability on improving taxpayers' voluntary tax compliance through influencing taxpayers' perceived legitimacy in tax offices in Mazandaran province of Iran. The accountability is here taken as ‘responsiveness’. Adopting mixed methods design, the Delphi technique was first used to identify the legitimate expectations and demands of taxpayers. In the second step, 4 types of accountability mechanisms were identified as the components of overall accountability. In the third step, using partial least squares path modeling via Smart PLS software, the impact of the tax system's accountability on the perceived legitimacy of the tax system as well as the impact of perceived legitimacy of the tax system on voluntary tax compliance was tested. The obtained results indicated that the tax system's accountability affects voluntary tax compliance through influencing taxpayers' perceived legitimacy of the tax system. Furthermore, political and social accountability was not at the optimal level and the optimality of managerial and legal accountability did not have a significant impact on voluntary tax compliance. Finally, it is suggested that to improve the perceived legitimacy of the tax system. As the results of voluntary tax compliance showed, more attention should be paid to the mechanisms of political accountability in the political sector and social accountability in both the political and administrative sectors of the tax system.