One of the main benefits of the clusters are higher innovative performance. Recent research shows that companies do not benefit from the cluster equally, firms who are in the right networks which have useful knowledge flows are more innovative. This brings up the question of “which knowledge sources are more effective for innovation?" Literature suggest that while knowledge sharing within the cluster is crucial, too dense relations will cause lock-in and external sources are vital for innovation, and; the knowledge sources vary according to the knowledge base of the clusters. This study examines the types of knowledge sources and their relation to innovative performance with a regression model. The research was applied to two clusters in Turkey which have synthetic knowledge base.