Micro-PIV measurements were implemented for laminar flows in 0.4 - 0.8 mm micro-channels under different conditions. In the measurements

3 μm fluorescent microspheres were chosen as the track particles

whose images were gained by using 532 nm laser

12 bit CCD and 10X objective. The process techniques of background noise were employed to improve SNR of images. The velocity vectors at the middle section of microchannels were achieved by the ensemble correlation and recursive arithmetics

and spatial resolving power of measurements reached 23.68 μm×23.68 μm×15.64 μm. The characteristics of velocity fields were analyzed by illustrating the space-averaged streamwise velocities in whole fields. The comparison of the averaged velocity with theoretical velocity profiles shows that velocity distributions are in accordance with their theoretical counterparts. In order to remove the stochastic distribution effects of wall surfaces

the fully-developed velocity distributions were determined by space-averaged method along the streamwise direction for the whole velocity field. Compared with the theoretical power function profile of velocity distributions in the square channels

the flow for the Micro-PIV measurements has the characteristics that the disturbances of velocity at the region near the walls have direct correlations with the scales of the microchannels. Execpt the areas near the walls

the space-averaged velocities are in agreement with the theoretical velocity profile.