Abstract A micro particle image velocimetry (micro-PIV) system was used to investigate the shape of the meniscus and the flow characteristics in open rectangular microgrooves heat sinks. In experiment, the rectangular microgrooves heat sinks were placed in horizon, the inclined angle of 15, 25 and 35°. The results show that the shape of meniscus in rectangular microgrooves heat sinks in horizon, the inclined angle of 15, 25 and 35° with input heat flux is parabolic. At low heat flux, the shape of meniscus in horizontal microgrooves heat sink could be regarded unchanged and never touches bottom of the microgrooves; in inclined microgrooves, the bottom of the shape of meniscus gradually moves downward to the microgroove bottom. Flow stages in rectangular microgrooves heat sinks verify the assumption that there exist continuous accommodation stage and corner flow stage. The mean curvature of meniscus in horizontal microgrooves almost does not change along axial direction of microgrooves. The mean curvature of the meniscus increases along the axial direction of inclined microgrooves heat sinks. Velocity decreases from the middle to both of the side walls. The mean velocity profile is not symmetrical, and this is due to the different roughness of two side walls.