Abstract The results of criticality, sensitivity and uncertainty (S/U) analyses on the 1st core criticality of the Indonesian 30 MWth Multipurpose Reactor RSG GAS (MPR-30) using the recent nuclear data libraries (ENDF/B-VII.1 and JENDL-4.0) and analytical tools available at present (Whisper-1.1) are presented. Two groups of criticality benchmark cases have been carefully selected from the experiments conducted during the first criticality approach and control rod calibrations. The C/E values of k (effective neutron multiplication factor) for the worst case is found around 1.005. Large negative sensitivities are found in (n,γ) reaction of H-1, U-235, Al-27, U-238, and Be-9 while large positive sensitivities are found in U-235 (total nu and fission), H-1 (elastic), Be-9 (free gas, elastic) and H-1 S(α,β) (lwtr.20t, inelastic). The energy dependency of the sensitivities is also presented and discussed in detail. From the S/U analysis, it is found that the uncertainties of k due to the nuclear data are about 0.6%, which are comparable to the [C/E−1] values. k Differences in the sensitivities amongst the two nuclear data libraries are also identified, and recommendation for improving the nuclear data library is given.