Pension as a motivational system by providing future financial security of employees has an important role in their job satisfaction and calmness; despite the importance of financial reporting of pension funds, their accounting standard not been thoroughly investigated. The purpose of this paper is assessing the effectiveness of Iranian Accounting Standard of Retirement benefit plans (No.27) and its overall evaluation using Post Implementation Review and mixed method; in other words, we used questionnaires and interviews for collecting data: 104 collected questionnaires were been analyzed by Fuzzy Delphi method; content analysis was also used to analyze the interviews. The results indicate that Standard No.27 has achieved its goals; Cost-benefit analysis also justifies the application of standard requirements. It is applicable to all pension funds, but approving appropriate accounting standards for other retirement benefit plans is necessary. As well as there are not essential infrastructures for applying Standard NO.27 in Iran. These infrastructures include Actuarial and tax issues, calculating fair value and legal and structural conflicts.