Objective. To assess the reliability and validity of the translated and culturally-adapted Institutional Review Board Researcher Assessment Tool (IRB-RAT) for Peruvian research ethics committees (RECs). Materials and Methods. The IRB-RAT is an instrument that determines how RECs are perceived by researchers based on eight factors, using two formats: 1) importance in the work of the researcher and 2) descriptive of the REC being evaluated. Its original English version was translated and culturally adapted into Spanish, with the support of experts and representatives of the target population. Then, according to the responses of 113 users, the heterogeneous items were identified and eliminated until a final version of 29 items was obtained. The reliability of this version was reviewed using Cronbach’s α and omega coefficient, its internal structure validity through a confirmatory factor analysis with the unweighted least squares method. Results. Translation and cultural adaptation complied with internationally recommended steps. Reliability at the level of the eight factors was moderate for format 1 (0.67<α<0.89; 0.71<ω<0.89) and high for format 2 (0.83<α<0.92; 0.85<ω<0.92). Content validity was high at item level and moderate for factors. Internal structure validity was good for format 1 (AGFI=0.97, GFI=0.97, NFI=0.97, RMR=0.04) and moderately good for format 2 (AGFI=0.99, GFI=0.99, NFI=0.99, RMR=0.10). Conclusions. Our Spanish adaptation of the IRB-RAT has sufficient reliability and validity to assist in the continuous improvement of the RECs in Peru and other Spanish-speaking countries.