This paper study the determinants of real exchange rate from an internal perspective using macroeconomic variables that can be endogenous. We used a GMM System estimator and we transformed our variables using forward orthogonal deviations (FOD) and first differences (FD). For check the robustness of our estimations, we used different sizes of observations. Our results show that terms of trade have negative and significant impact for all sizes. The gross domestic product has positive and significant impact and the rest of variables has mixed effects depending the sizes observations.