This work investigates the effect of urea injection parameters on the reduction of NOx emissions from a 4-stroke twin-cylinder diesel engine fueled with neat biodiesel. The test plan was designed by employing L-9 (3(4)) Taguchi orthogonal array. It has been experimentally found that the concentration of urea, the flow rate of urea and increase in spray angle has a significant effect on reducing in NOx emissions of the diesel engine when fuelled with neat biodiesel. Further, ANOVA results reveal that the concentration and flow rate of urea are the major parameters in reducing NOx emissions whereas, mixing length and spray angle have minimal effect on reduction in NOx emissions. Since the predicted value derived from Taguchi technique is in accordance with the test results from the confirmation test, the predictive capability of this technique in the study shall be inferred.