Microchannel heat sinks have been widely utilized in micro fuel cells, micro medical equipment, high power cooling systems and so on. Fabrication of porous structures on the micorchannel surfaces provides an efficient method to enhance heat transfer, as it enlarges the heat transfer areas considerably. In the study, a laser micro-milling method is used to fabricate porous structures with micro-holes and micro-cavities on the microchannel wall surfaces. Three different shapes of micro-channels, i.e., U-shaped, V-shaped and rectangular ones, were utilized to process the porous structures, which demonstrated that porous structures can be formed on all the microchannels. Besides, the effect of laser fluence on the formation of porous structures on the rectangular microchannels was also explored. It was found that laser fluence played a vital role on the formation of porous structures. With the increase in laser fluence, the cross-sectional shape of the rectangular microchannels changed from rectangular to trapezoidal one. The channel depth and surface roughness of porous copper surfaces increased, whereas the channel bottom width decreased with increasing the laser fluence.