There is an ever-increasing discussion on project governance in recent project research, but relatively little attention has been paid to the informal relationships in the governance despite their importance in Chinese business affairs. In this study, we investigate the impact of informal relationships in governance on the software project success. An exploratory case study was used to explore what was meant by informal relationships and how these relationships impacted the project success involving formal governance. Three major determinants of informal relationships were identified: cooperation norms, trust and stakeholder relationship. A set of propositions for the impacts of the governance, including informal relationships and formal mechanisms, on the project success were also developed.