As one of Indonesia's largest state-owned construction companies, PT Waskita Karya has adopted Good Corporate Governance (GCG) standards based on the ASEAN Corporate Governance Scorecard and guidelines from the Financial Services Authority (OJK). While the company has consistently achieved a "Very Good" rating in recent years, GCG implementation on the ground continues to face significant challenges that affect its effectiveness. This study aims to evaluate the quality of GCG implementation at PT Waskita Karya through an internal marketing approach and identify issues and deviations within the company. This research employs a qualitative methodology using content analysis of secondary data, including annual reports, media coverage, and official press releases. The findings reveal that weak internal oversight has created opportunities for corruption and financial report manipulation. These practices have not only eroded stakeholder trust but also damaged the company’s reputation in the market. Furthermore, the internal marketing approach has not been fully optimized, as evidenced by a lack of transparency and interdepartmental collaboration. This deficiency hampers the company's synergy in achieving shared strategic objectives. The study concludes that to foster more accountable and transparent governance, PT Waskita Karya must strengthen internal synergy through the application of internal marketing. This approach integrates all company functions to work cohesively, thereby improving cross-departmental coordination and supporting decision-making aligned with GCG values. Theoretically, this research makes a significant contribution by suggesting that integrated GCG implementation, supported by internal marketing, enhances governance practices while building sustainable trust and transparency. This effort is crucial in supporting long-term growth grounded in the trust of stakeholders and the broader community.