The GUTMAM Radioactivity Measurement and Analysis Laboratory, operating under Gazi University Central Laboratory Application and Research Center for Fundamental and Engineering Sciences, has once again proven its high analytical competence on an international scale by receiving an A score in all radionuclide measurements conducted on various sample matrices in the International Proficiency Test program (coded IAEA-TERC-2025-1), organized by the International Atomic Energy Agency (IAEA) in 2025 with the participation of 550 laboratories. Within the scope of the said proficiency program, the laboratory conducted comprehensive analyses for the determination of naturally occurring and anthropogenic radionuclides on soil samples with different compositions, plant samples, water samples, and simulated filter paper samples used for contamination monitoring. In these analyses, radionuclides belonging to the uranium and thorium decay series, natural radionuclides such as ²¹⁰Pb, ²²⁶Ra, and ⁴⁰K, as well as anthropogenic radionuclides such as ¹³⁷Cs, ¹³⁴Cs, ¹³³Ba, ²²Na, and ⁶⁰Co were determined with high accuracy. The measurement and evaluation studies were carried out using the Ortec brand high-purity germanium (HPGe) gamma spectrometer available in the laboratory. The methods applied in analyzing gamma emitters within samples containing multiple radionuclides were executed in compliance with the evaluation criteria defined by the IAEA in terms of measurement accuracy, uncertainty management, and traceability, and all analyzed radionuclides were accepted with an A score, representing the highest performance level. These results clearly demonstrate that the GUTMAM Radioactivity Measurement and Analysis Laboratory is capable of performing reliable, reproducible, and internationally compliant measurements across numerous sample matrices with diverse physical and chemical properties. This achievement reinforces the strength of Gazi University's scientific infrastructure in environmental radioactivity and nuclear analytical applications, while positioning GUTMAM as a reference radioanalytical laboratory on both national and international scales.