The long-term operation of power plants can cause changes in the properties of structural materials. To ensure the safe and reliable operation, it is necessary to monitor and evaluate these changes. Samples for standard mechanical tests are quite large and their availability is limited. The Small Punch Test (SPT) method can be used to evaluate the mechanical properties from a small volume of obtained material, which can reduce radiation exposure during testing of irradiated samples. This method is currently undergoing a standardization process both CEN and ASTM. This paper presents the results of the round-robin tests of the SPT method, carried out in the three different labs, on the materials from the power plant components. On the basis of the obtained results, the influence of the test matrix geometry and production accuracy was evaluated, as well as the defined test parameters.