This study analyzes the network structures of institutional shareholders and examines the influence of institutional investor cliques on corporate innovation. Our empirical results reveal that institutional investor cliques significantly enhance both innovation input and output. To mitigate endogeneity concerns and establish causality, we adopt multiple empirical strategies. Further evidence suggests that the beneficial impact of institutional investor cliques on firm innovation can be attributed to increased innovation investment efficiency, enhanced employee productivity, reduced information asymmetry, and decreased managerial myopia. Additionally, we find that the positive effect of institutional investor cliques on firm innovation is more pronounced in non-state-owned enterprises and is particularly evident in firms with severe agency conflicts, CEO duality issues, highly competitive product markets, and for firms that have low stock liquidity.