Abstract: The flow rate and swirl characteristics of the injector for the urea-SCR that are varied according to design changes were examined through an unsteady-flow analysis. The design parameters that were taken into account for the improvement of the intra-injector flow characteristics are the number of swirl passages, the nozzle-curvature radius and the length of the needle-end shape. The characteristics of the internal-flow rate were analyzed and the amount of the single-injection flow rate of the injector appeared to increase in accordance with the increasing of the number of swirl passages, the increasing of the nozzle-curvature radius and the decreasing of the length of the needle-end shape. The corresponding swirl characteristics were also analyzed and the swirl-disk-created rotary flow affected the outlet flow with a continuous increasing of the swirl coefficient until the termination of the injection. The average swirl-coefficient values were compared and the results indicate that a lesser number of swirl passages, a bigger nozzle-curvature radius and a longer needle-end shape are advantageous for the enhancement of the swirl intensity. The analysis of the urea-SCR injector that was conducted in this study is likely to be exploited as a basic study for the design and performance enhancements of single-swirl injectors.