The flow characteristics of deionized water and kerosene through smooth rectangular microchannels with varying hydraulic diameters are studied experimentally. Through the special design of the experimental setup, a wide range of measured average liquid velocities in microchannels is achieved, corresponding to broad-ranging Reynolds numbers. The experimental data indicate that the pressure drop exhibits a linear relationship with the average velocity of the fluid in microchannels whose scales are larger than 2 mm. Moreover, the experimental Darcy friction factor is consistent with the classical laminar flow theory of a Newtonian fluid. Microscopic particle image velocimetry was applied to measure the velocity distribution inside the macrochannels. The experimental results agree well with the classical hydrodynamic theory.