The effect of length scale on turbulence and micro-fluidic mixing was investigated theoretically from first principles and experimentally using a micron-resolution Particle Image Velocimetry (PIV) system. It was determined that turbulence in micro-systems − where the characteristic length scale is less than 10-3 m − the typical three region turbulence model breaks down as large and small eddies become indistinguishable and the presence of turbulent eddies in the near-wall region is entirely possible. Furthermore, micro-scale turbulence may be more accurately modeled as a single fluid region where the range of turbulent eddy size is very narrow and is therefore difficult to induce. Imaging and velocity vector measurement for mixing flows in micro-channels with cross-sections of 200 × 75 µm and 2000 × 75 µm quantified earlier findings in the literature that undisturbed mixing of low pressure, low velocity micro-flows occurs only by molecular diffusion. This experimental work does, however, lay a foundation and develop a control for further investigation of micro-scale turbulence and fluidic mixing establishing that pressure driven micro-flows at low system pressures, despite relatively large values of surface roughness, have no tendency to mix via turbulent motion.