本篇論文目的在檢視壽險業資本結構的影響因素，樣本為美國壽險公司。金融及保險市場的特殊性質會造成保險公司有動機去調整控制資本結構與資產風險，以維持公司失卻清償能力的風險在適當的範圍內。我們的實證結果中顯示槓桿比率與資產風險的負向關係的確存在於美國壽險業當中。 此外，一般公司資本結構理論中的公司大小、代理問題皆顯示對壽險公司的資本結構造成影響；公司的評比對公司的槓桿比率有顯著影響；使用獨立代理人銷售業務的公司有較高的槓桿比率與風險；實證結果亦顯示壽險公司的資產風險與投資的集中度及經營險種的集中度有正相關，意味著資產風險可以透過分散投資與險種多樣化的方式來分散降低。 / This study examines the capital structure determinants of life insurance companies in U.S. The decision of capital structure in insurance industry should be a joint decision of capital structure and firm risk. Insurers have incentive to keep firm risk within a safe range, due to the special features in the insurance markets. We find evidence supporting the negative relationship between leverage ratio and firm risk, suggesting that insurers will balance risk and leverage to keep the insolvency risk within a desired range. In addition, general capital structure theories such as size and agency theory are significant in our empirical result. Rating is shown a significant factor of capital structure in life insurance industry. Evidence suggests the independent agents have less incentive to monitor insurers. Firm risk is also shown significant relationship with undiversified investments and concentrated business line, which suggests that life insurers can reduce firm risk by diversifying investment risk and business risk.