The paper studies optimal debt maturity structure and focuses on two questions: whether firms of different leverages can increase firm values by exploiting short-term and long-terms bonds and/or by dispersing debt maturity dates. The calibrated model shows that it is optimal for low leverage firms to use long-term bonds exclusively but for high leverage firms to use a mixture of two types of bonds; a more dispersed maturity structure increases firm value regardless of leverage and average maturity. The economic reasons for the results are discussed. The model reveals an intricate relationship between leverage and debt maturity structure.