Abstract: To increase the security of delegation, an attribute-based delegation model called ABDM\-A is presented, which is an extension of current delegation models. Delegation constraint in ABDM\-A consists of both delegation attribute expression (DAE) and delegation prerequisite condition (CR). Delegatees must satisfy delegation constraint (especially DAE) when assigned to a delegation role. For a better flexibility, delegation attribute expression is divided into two types: permanent and temporary delegation attribute expressions. With temporary delegation attribute expression, the delegator can temporarily, not permanently, delegate high level permission to low level delegatees. ABDM\-A relieves the security management effort of the delegator and the system administrator in delegation and increases the security of delegation.