This research aims to examine the validity of purchasing power parity theory in four main currencies towards Rupiah, namely US Dollar-Rupiah, Yen-Rupiah, Poundsterling-Rupiah, and Euro-Rupiah. The Purchasing Power Parity theory (PPP) postulates that the fluctuation of exchange rate is influenced by the fluctuation of inflation differentials between two countries. Types of research used in explanatory research with quantitative approach. Sampling method in this research using full sampling based on quarterly time series data since January 2003 until June 2013 which is consist of 42 samples. This research used simple linear regression analysis as technique of analysis. According to the result of regression and partial test (t test), in US Dollar-Rupiah and Poundsterling-Rupiah obtained results are in accordance with purchasing power parity theory, while in Yen-Rupiah and Euro-Rupiah obtained result that are not in accordance with purchasing power parity theory.