The study examined the effects of financial risk, firms'' characteristics and macroeconomic factors on the capital structure and the rate at which firms adjust towards their target capital. Secondary annual panel data for the period of 1990 to 2006 using 70 non-financial listed companies for analysis were employed. Data were sourced from the Annual Report and Accounts of the sampled firms and the publications of Central Bank of Nigeria. Descriptive method and Generalized Method of Moment (GMM) were used to analyze data. The results indicate a positive coefficient between financial risk and capital structure and those Nigerian companies with higher financial risk tend to use more short-term debt in general. Also, profitability, tangibility, corporate tax rate, age of the firm, earning power, volatility, inflation and foreign direct investment, have significantly positive effects on capital structure. In addition, thirty-eight firms adjust fully to their target capital, while thirty-two over adjust. The study concluded that effective financial risk management and good financing policy decision would greatly improve firms'' performance in Nigeria.