In this paper we propose a theoretical model to assess the effectiveness of mobile work support by investigating the fit between mobile task and mobile work support. The mobile task has been investigated along five dimensions: task difficulty, task interdependency, time-criticality, mobility, and location dependency. The functionality of mobile support technology is categorized along five dimensions: portable processing power, mobile communication, mobile online information access, mobile job dispatch, and location-aware services. Propositions are proposed for testing the impact of the fit between mobile task and mobile support on the performance of mobile worker.