We investigated the large-scale connection between African aerosol and precipitation in the West African Monsoon (WAM) using both monthly and daily MODIS aerosol product (aerosol optical depth, fine mode fraction) and TRMM precipitation and rain type. Study proves the existence of a large-scale link between aerosol and precipitation although this link has distinct seasonal and spatial variability. A composite analysis based on monthly data indicates that precipitation is suppressed significantly in central WAM region when aerosol is high in boreal cold season. Such suppression happens in both deep convective and stratiform rain, but cannot be clearly observed in shallow convection. Both dust (coarse mode aerosol) and smoke (fine mode aerosol) contribute to the suppression; however, dust effect is more reflected in the Gulf of Guinea while smoke suppresses precipitation both on land and over the ocean. The observed precipitation reduction cannot be linearly attributed to major climate factors and ambient moisture. A further back trajectory and regression analysis using daily aerosol and precipitation data statistically illustrates a link between precipitation reduction and upwind aerosol concentration. This study suggests that African aerosol outbreaks in the WAM region can influence precipitation in the local monsoon system which has direct societal impact to local community. It calls for systematic investigation using both observational and modeling approaches to determine the modulating mechanisms.