Insurance companies have an important function of absorbing and storing economic risks. Therefore, companies need to have optimal, safe, and stable capital sources to be able to finance, diversify, and transfer risks. Previous studies have only focused on market share, customers, competitive strategies, and insurance premiums without paying attention to the capital sources of insurance companies. This is more necessary when Vietnamese insurance companies have a non-optimal capital structure, leading to low profitability. The study aims to fill the above gap by analyzing the impact of capital structure on the profitability of insurance companies through the research sample of the Data Set of 40 insurance companies (listed on HNX, HOSE, UPCOM), corresponding to 297 observations in the period from 2013 - 2023. By using GMM estimation, the author has identified three independent variables explaining (and two control variables) the variation of the dependent variable profitability (ROE), including (i) General debt ratio (GDR), (ii) Debt ratio (DR), (iii) Long-term debt ratio (LDR). Based on the research results, the authors discuss and assess the important role of capital structure in insurance companies and provide financial solution recommendations to improve their profitability.