The 30 MW RSG-GAS reactor, is routinely operated with a cycle of 600 MWD. At the end of the cycle, a new reactor core is built for the next cycle operation. Twelve fuel elements are taken out from the core. Then, the fuel elements are inserted one by one until a certain excess reactivity is achieved, according to loading steps from calculations. The research aims to evaluate the criticality experiment data of the reactor core by calculation using the new cross-section data generated from the newest ENDF/B-VIII.0 by Serpent 2. The calculations were done by the Batan-FUEL code. By using the existing cross-section, the critical conditions occurred at insertion step no. 3, while with the new cross-section critical occurred at step no. 4. The experiment reaches critical conditions at step no. 5. It shows that criticality calculation results are closer to the experiment value when using the new cross-section data.