Vietnamese Government set an ambitious economic growth target of 8% for 2025, aiming to pave the way for potential double-digit expansion in the coming years. At the 2024 Green Economy Forum, Vietnam reaffirmed its commitment to sustainable development, emphasizing that economic growth must be aligned with social equity and environmental sustainability, and highlighting the critical role of green energy and coherent ESG practices at the firm level. As the backbone of the economy and key agents in the energy transition, energy companies are uniquely positioned to contribute to this agenda. They not only supply power for economic development but also bear the responsibility of transitioning toward sustainable energy sources. In this context, ESG has become a critical consideration for firms in the energy sector. This study investigates the impact of ESG disclosure on the cost of capital of Vietnamese energy companies. Using firm-level panel data and third-party verified methodology, we employ GMM to examine both the direction and significance of this relationship. The findings indicate a statistically significant linkage between ESG disclosure and the cost of capital, suggesting that enhanced transparency in ESG practices may reduce financing costs. Based on these results, the paper offers practical recommendations for policymakers, companies, and investors aiming to promote sustainable growth through better ESG integration in the Vietnamese energy industry.