Optimum safety and reliability can be achieved by coordinating an interlaboratory proficiency testing among different laboratories. Testing laboratories need to verify their test procedures and testing capability for reliable results. In this study, equivalent samples are prepared by cellulose based transformed board material used in transformers as electrical isolation material. Randomly selected test samples having specified dimensions are sent to the participant laboratories. Then they are tested and results are analyzed according to previously defined parameters. Each laboratory applied tensile and flexural tests on the samples according to procedures given in IEC 60641-2, 2004 and IEC 60763-2, 2007 standards respectively. Test results are evaluated according to same procedures explained in related standards by the participant laboratories. TUBITAK UME Material Testing Laboratory being the pilot laboratory collected to the all evaluated results including associated measurement uncertainties. Then the collected results evaluated according to ISO 17043, 2010 are reported by each laboratory as a part of the proficiency test report. Z-scores of the participant laboratories are presented.