In this experimental study, effects of ethyl alcohol-water mixtures as reducing agents in the presence of Ag/Cu-based catalyst on NOx conversion efficiency were investigated. The Ag/Cu-based catalyst was synthesized with the impregnation method. In this method, cordierite structure was immersed into the solution including nanoparticle materials and then the solvent was evaporated. The analysis done by SEM and XRD revealed the structural and chemical properties of the catalyst. In order to obtain information on how the addition of water affects the activity of the NOx conversion in the SCR exhaust test performance system, tests were carried out depending on a temperature window of 170-260 degrees C, two different space velocities (20000 h(-1), and 40000 h(-1)), and three different reductants (100% Ethyl alcohol (E), 4% water + 96% Ethyl alcohol (E4 W), and 8% water + 92% Ethyl alcohol (E8 W)). The increase in the engine load showed a little increase in the NOx conversion rates. Taking into account the space velocity, the NOx conversion rates were higher at 20000 h(-1) in comparison at 40000 h(-1). The highest NOx conversion rate recorded in the tests was 68% at 4 kw engine load, 100% ethyl alcohol spraying, and 20000 h(-1). However, the results of the tests showed that when the water content of the reductants increased from 4% to 8%, the NOx conversion rates decreased at both 20000 h(-1) and 40000 h(-1) SV. The highest NOx conversion rates of the tests conducted with E4 W and E8 W reductants were 62.75% and 61.78%, respectively, at 4 kw engine load and 20000 h(-1). Also, the highest NOx conversion rates of the same reductants were 55.8% and 55.01%, respectively, at 4 kw engine load and 40000 h(-1). It was concluded that the water added to ethyl alcohol has a negative effect on NOx reduction.