Abstract: In mobile ad hoc networks (MANETs), mobile nodes share resources and collaborate to do work by using Web service technologies, and the service is defined as any hardware or software entity that resides on a mobile device or platform. However, the complex environment, dynamic network links and heterogeneous terminals make the service availability constantly vary and be difficult to assess in quantitative model. In this paper, after analyzing the running environment of services and the environmental factors that impact the service availability, an environment-aware quantitative assessment model for service availability (EQAM-SA) is proposed, which is touched off by the service requesting. In EQAM-SA, the running parameters of services are obtained and the quantitative evaluation indicators are then computed in real time as soon as a service request is received. The weights of these indicators are different and are used to assess services availability in different application scenarios, so Delphi approach is used to determine the weights. Then, the analytic hierarchy process (AHP) approach and multi-attribute evaluation with a weighted sum model are adopted to evaluate the service availability. Finally, the feasibility and effectiveness are validated by numbers of simulations.