MEMS-based microneedles have the potential to revolutionize biomedical/biotechnology applications by providing precise transdermal drug delivery and localized blood sampling. In this paper, we propose a novel theory-based model that predicts drift velocity of blood-flow through the microchannels embedded in the microneedles. The profile of blood flow in the microneedles is determined by solving the conservation of momentum equation of the liquid phase, coupled with the force balance equations at the liquid-air interface. For the first time, this work enables accurate calculation/prediction of the velocity profile of the blood flow through a vertical in-plane microneedle, considering the effect of surface tension forces which are the most prominent forces. In order to withdraw blood samples from capillaries in the dermis layer, the length of our MEMS-based in-plane microneedle has been set at 600 μm with the micro-channel thickness chosen to be 35 μm, to avoid deformation of red blood cells. Blood flow through microneedles has been computed analytically using the proposed formulation. The results are then verified by a commercial finite element simulation tool "ANSYS".