Purpose: Management of inter-organizational projects focuses on the collective benefits of a group of organizations on a shared activity for a limited period and the coordination among them. However, how learning is facilitated in the inter-organizational project remains under-developed in the literature. Design/methodology/approach: This research analyses the exploitative learning process in the longest tunnel project on land in the Netherlands realized in a densely populated area. Data were collected through archived documents, in-depth interviews, site visits in the ethnographic research to analyze the actors, the daily practices and social situations in projects. Findings: The empirical findings indicate that exploitative learning is promoted positively between the owner and the contractor and internally within the contractor. The most significant change that the exploitative learning process has led to is the change in mindset toward the collaboration. Project culture is considered to be shaped by exploitative learning in the inter-organizational project. However, there is a gap between the transfer of knowledge from the inter-organizational project to the parent organization. Originality/value: The findings have implications for understanding learning in the inter-organizational project setting.