Thermal and flow characteristics of the micro-channel water-block with pass variations in 8 samples were studied. Results of a numerical analysis using the CFX-11 were compared with results of experiments. Numerical analysis and experiments were conducted under the conditions, input power of 150 W, inlet temperature of 35 ? and mass flow rates of 0.7 ~ 2.0 kg/min. The numerical results showed reasonably good agreement with the experimental results within 3 ~ 5%. Also, the numerical results showed that the sample 2 types with the 2 pass gave better performance than the sample 1 types with the 1 pass from the viewpoints of heat transfer and pressure drop.