Theoretical and experimental studies of the heat transfer enhancement have been made for a laminar air-water mist flow impinging on an isothermal plate. The governing boundary-layer equations for this problem are solved by the Van Dyke's Matching Method. The mechanism of the heat transfer enhancement can be separated into two parts: (l)an enhancement function ø1, pertaining to water droplets that mix with air stream in the flow field; and (2)another enhancement function ø2, representing water droplets that separated from the main-stream due to the inertia, impacting on the heated wall and then evaporating. The sum of ø1 and ø2 is related to the ratio of the average Nusselt number of the present two-phase flow with that for one phase flow in the form: Nu/Nuo=l+ø1+ø2. Experimental heat transfer data for various mass flow rate of water, wall temperature and air-water mist flow velocity have been obtained. The theoretical solution compared favorably with the experimental data obtained in this study.