Role-Based Access Control(RBAC) model is becoming a promising model for enterprise environments with various organization structures. In terms of role hierarchy, each senior role inherits all the permissions of its junior roles in the role hierarchy, and a user who is a member of senior role is authorized to carry out the inherited permissions as well as his/her own ones. But there is a possibility for senior role members to abuse permissions. Since senior role members need not have all the authority of junior roles in the real world, enterprise environments require a restricted inheritance rather than a unconditional or blocked inheritance. In this paper, we propose a new role-based delegation model using the role hierarchy model with restricted inheritance functionality, in which security administrator can easily control permission inheritance behavior using sub-roles. Also, we describe how role-based user-to-user, role-to-role delegations are accomplished in the model and the characteristics of the proposed role-based delegation model.