This paper examines how firms’ R&D disclosures are associated with collaborative innovation, measured by co-patenting intensity. Compared to solo patents, co-patents are more uncertain and face a greater risk of proprietary information leakage. We find that firms with more co-patents tend to disclose less R&D information in 10-K filings, particularly when they collaborate on existing knowledge or in their core business. The association is stronger when firms’ IP rights are weakly protected. These findings suggest that firms tend to keep R&D disclosures low when they share essential knowledge and when competitors’ value appropriation is more likely. Lastly, we investigate alternative mechanisms (i.e., responding to investors’ information demand, signaling incentives, and expanding the collaborative network) that could affect the relationship between co-patenting and R&D disclosures. Altogether, our paper underscores collaboration as a key influence on corporate disclosures.