A numerical and experimental study of three-dimensional steady incompressible non-reacting flow inside various dual-monolith catalytic converters has been conducted for achievement of performance improvement, reduction of light-off time and longer service life by improving the flow uniformity within the monolith. In this study, the effects of curvature of inlet exhaust pipe and monolith brick length on the flow uniformity and pressure drop within monolith were numerically investigated. The computations are confirmed by measurements of steady flow. The agreement between computations and experiment was relatively good. The result of this study shows that curvature of inlet exhaust pipe and monolith brick length gave a great effect on the flow uniformity and the shorter the brick length, the lower flow uniformity and the less pressure drop.