Many protocols have been proposed for solving the user authentication in portable communication system. One of the schemes is based on the delegation concept. Home Location Register (HLR) delegates Mobile Station (MS) to be authenticated by Visitor Location Register (VLR). The main drawback of the scheme is that the HLR is required during the online authentication phase between VLR and MS. In this paper, a double delegation-based authentication and key agreement protocol is proposed. The main advantage of our protocol is that this scheme requires only MS and VLR online. This protocol will thoroughly utilize the proxy signature features to facilitate the operation of this protocol while only requires two members (MS, VLR) to be online at the same time.