In the present study, the effects of Reynolds number on the flow characteristics around rectangular cylinders in uniform flow with length-to-height aspect ratios (AR) of 1 and 4 were examined experimentally using particle image velocimetry. High spatial resolution experiments were performed at Reynolds numbers of 3000, 7200, 14700 and 21000 for each aspect ratio. The results show that the separated flow is directly shed into the near wake region for AR1, while mean flow reattachment occurs on AR4, irrespective of the Reynolds number. The characteristics of the primary, secondary and wake vortices formed around the cylinders show dependency on both aspect ratio and Reynolds number. The streamwise mean velocity, turbulence intensities, transport of turbulent kinetic energy by fluctuating velocities in terms of quadrant analyses are also discussed. One-dimensional profiles are presented to quantitatively assess the effects of Reynolds number and aspect ratio.