ABSTRACT Extant research has shown equivocal evidences of brokerage on firm innovation. We try to unpack the mixed findings by studying how network density among a firm's alliance partners influences exploratory innovation. Based on the idea that it is optimum for a firm to focus on one type of innovation when searching for resources from the alliance network, we posit that a low level, as well as a high level of network density, offer a suitable environment for exploratory innovation, but a medium level of network density is more conductive to exploitative innovation. A longitudinal investigation of 277 biopharmaceutical firms indicates a U-shaped relationship between network density and exploratory innovation. This relationship is positively moderated by absorptive capacity. The study integrates related theories and provides a comprehensive framework of how the connect tightness among a firm’s partners impacts its exploration and exploitation behaviour.