Abstract: This study is conducted aimed to investigate the role of professional conduct of tax auditors in reducing tax evasion from the viewpoint of Isfahan Tax Affairs Experts. The study method is applied regarding the purpose the purpose, regarding the nature, it is descriptive-survey and the study sample consisted of all Tax Affairs Experts of Isfahan in December 2015 as 576 people. The sample size was calculated as 230 people based on Cochran’s formula and to select the sample convenience sampling method was used. Theoretical basics of the research were collected through library method and data was collected by field method using a researcher-made questionnaire in form of a five-item Likert scale. After distributing and collecting the questionnaires, 207 analyzable questionnaires were used for the analysis and evaluation of the hypotheses. Face and content validity of the questionnaire was verified by surveying the relevant experts and construct validity through confirmatory factor analysis and the reliability was tested and approved by calculating Cronbach’s alpha coefficient (Cronbach’s alpha coefficient was 0.967). The results showed that the components of professional conduct of tax auditorors that include “secrecy, observing professional standards and principles, professional competence and caring, honesty, good-temperedness and impartiality” have a role significantly more than the average in reducing tax evasion. Friedman ranking test results also showed that the components “impartiality,” “secrecy,” “honesty,” “professional competence and caring,” “observing professional standards and principles” and “good-temperedness” in terms of affecting reducing tax evasion rank first to sixth, respectively.