The international standard, ISO/IEC 17025 was developed to determine technical competence and to evaluate laboratories throughout the world. Accreditation bodies playing a vital role are increasingly using proficiency testing methodology as a tool to ensure the credibility of their accreditation programs. The successful completion of a well-designed proficiency test can validate the measurement method and uncertainty budgets of a testing laboratory. Additionally, proficiency tests can provide a good indication about the quality of the test results. An important part of inter-laboratory comparisons and proficiency testing is the determination of the associated error analyses which are focused on uncertainty values. This paper presents the implementation of proficiency tests using inter-laboratory methodology among five different acoustic laboratories. These tests were carried out on 5.27 KWCooling standard unitary air conditioner, A/C, such as through-wall or split room standard A/C units, for the assessment of Housing & Building National Centre acoustic laboratory. Analyses of results show a good agreement for En-Value among the selected laboratories when compared with the lowest uncertainty as stated by proficiency tests standards.