The mixing characteristics of a multi-holed static mixer have been studied for Newtonian fluid. A multi-holed static mixer composed of five pairs of 4- and 5-hole elements. The size of straight part of the hole, a, was changed in two steps of 2 mm and 5 mm and its inlet and outlet size, d, was also changed in two steps of 4 or 6 mm in the cases of a = 2 rum. The fluid viscosity and flow rate were also changed as parameters. Flow visualization experiments in a test pipe with 18 mm diameter were performed in order to observe the occupation ratio of dyed fluid, which is injected from the nozzle with 4 mm diameter mounted in the upstream of the static mixer. From the results, it is found that the Reynolds number based on the mean velocity in the 4 hole element and the hole size, Re-s, multiplied by a delivery ratio of the hole, d/a, well correlates the mixing and pressure loss characteristics. This is because there exist two mixing processes in the present static mixing system. One is the mixing process in a small hole by accelerated flow and the other is a delivery effect between holes.