This dissertation intends to study the relationship between commodity prices and real effective exchange rate for countries which exports portfolios accounts on a large share of commodity related products. In fact, all the four countries we study (Australia, Canada, New Zealand and Brazil) depends heavily on commodity exports, and therefore commodity prices might be important determinant of their terms of trade, becoming fundamental variable to the real exchange rate determination. It is also of great importance the careful treatment of the technical issues related to the study, so as to provide consistent estimates of the coefficients of interest, mainly when we consider all the divergence related to what the true data generating process of the series and the endogeneity of the commodity price index. To solve this issue we follow considering different assumptions, and for each we use appropriate econometric technical and then compare the results.