The influence of channel depth on the performance of a micro-separator/classifier (Ookawara et al., 2003), whose main section is a curved microchannel with a rectangular cross section, was studied experimentally and numerically. The width of the examined microchannel was 400 mum and the depths of three models (400a, 400b and 400c) were 250 mum, 170 mum and 100 mum, respectively. Suspensions with weight concentration of 0.06 wt% were prepared as test fluids using ion-exchanged water and acrylic polydisperse particles with average diameters of 7 mum, 10 mum and 20 mum, respectively. For the 7 mum particles, none of the models provided sufficiently high classification, although 400c showed a high concentration effect. The high concentration was possibly caused by the balance of extremely high centrifugal acceleration and a weak Dean vortex that enhances mixing and redispersion of concentrated particles near the outer wall. For the 10 mum and 20 mum particles, 400b always showed better performance than 400a because of the higher centrifugal acceleration in 400b and similar Dean vortex intensities. It is concluded, based on these results, that the channel depth is one of main factors that influence the performance of the micro-separator/classifier.