The effect of channel width and channel spacing on the flow distribution in a microfluidic device with U-type manifolds is numerically analyzed in this paper. Analysis is performed for flow rates between 1 ml/min and 60 ml/min. Flow distribution in a microfluidic device with three different microchannel widths are studied: 50 μm, 100 μm, and 200 μm. Reduction in the microchannel width reduced the non-uniformity in flow rate. Moreover, the flow malidistribution increased with increase in flow rate. The RMS value of the deviation of flow rate per channel reduced from 3 ml/min to 0.3 ml/min with reduction in channel width for a total flow rate of 60 ml/min. The effect of channel spacing on flow distribution was investigated for three channel spacing of 300 μm, 100 μm, and 50 μm. Reduction in channel spacing increased nonuniformity of flow distribution. The RMS value of the deviation of flow rate per flow rate reduced from 1 ml/min to 0.6 ml/min with increase in channel spacing for the greatest flow rate. From the particular studies examined in this paper it is found channel width has a stronger influence on flow distribution than channel spacing. Moreover, proper selection of channel width and channel spacing can uniformly distribute flow.