Experiments were performed using a microparticle image velocimetry (MPIV) for full field velocity distributions of electroosmotically driven flows in a 40 mm long microchannel with a square cross section of 200 µm ¡Ñ 200 µm. Electroosmotic flow bulk fluid velocity measurements were made in a range of streamwise electric field strengths from 5 to 25 kV/m. A series of seed particle calibration tests can be made in a 200 µm x 200 µm x 24000 µm untreated PDMS channel incorporating MPIV to determine the electrophoretic mobilities in aqueous buffer solutions of 1 TAE, 1 TBE, 10 mM NaCl, and 10 mM borate, respectively. A linear/nonlinear (due to Joule heating) flow rate increase with applied field was obtained and compared with those of previous studies. A parametric study, with extensive measurements was performed with different electric field strength and buffer solution concentration under a constant zeta potential at wall for each buffer. The characteristics of electroosmotic flow in square microchannels were thus investigated. Finally, a composite correlation of the relevant parameters was developed within accuracy for 99% of the experimental data.