Social impact assessment (SIA) is a topic very important to prevent environmental conflicts. Particularly, in Peru there are many social conflicts from the implementation of mining projects. In this work, SIA was conducted using the grey clustering method, which is an approach based on grey systems theory. The grey clustering method can be applied by incidence matrixes or whitenization functions; in this study, we applied center-point triangular whitenization weight functions (CTWF). In turn, a case study was developed on a mining project located in Cajamarca, Peru. In case study, seven evaluation criteria were established. The results revealed that the project would have normal social impact. In addition, the criterion more controversial was access to drinking water. Consequently, the method showed quantitative and qualitative results that could help central and local governments to make the best decision on the mining project. Moreover, the grey clustering method showed interesting results that could be apply to SIA from other projects or programs.