A three-dimensional computational method is employed to study the flow and heat transfer in internally finned tubes with a multilobe vortex generator inserted. Governing equations are discretized using the finite volume method. The irregular lobe geometry is treated using curvilinear nonstaggered grids. The linear interpolation method is adopted to calculate face velocities. The results show that secondary flows induced by the lobes are transformed to become axial vortices downstream of the vortex generator. As a consequence of the transport by the vortex flow, the core flow is moved to the fins and the tube wall, while the wall flow moves to the core. In this way, both heat transfer and flow mixing are enhanced. When the fin height is increased, the axial vortex is more restricted in the centerline region, and the strength of the vortex flow, represented by circulation, is decreased. In turn, the total pressure loss is also decreased. However, the heat transfer increases with fin height. Consequently, efficiency is greatly promoted.