The purposes of this study are to propose an experimental method for predicting the long-term Ca leaching from concrete and the deterioration of concrete caused by Ca leaching. This method consists of a combination of electro-chemical test and diffusion test. And the estimated years of Ca leaching can be obtained by using a technique combined the results from electro-chemical and diffusion tests. Also, the concrete deterioration caused by Ca leaching can be predicted by examining the specimen after Ca leaching. The validity of this method is verified comparing the prediction results with the investigation of an existing structure used for 100 years. Finally, the influence of mix proportion upon the concrete deterioration caused by Ca leaching is investigated using this method.