The aim of this work was to evaluate the emission of nitrous oxide (N2O) using a diesel engine at laboratory scale without a catalytic converter with diesel/biodiesel blends (%) of 95:5 (B5), 90:10 (B10), 85:15 (B15), 80:20 (B20), 75:25 (B25), and 50:50 (1350). Measurements of N2O in the exhaust gas were made using an experimental setup based on photoacoustic spectroscopy using a quantum cascade laser that was validated to be selective and sensitive in the range from 1.7 to 2.72 ppmv. According to the experimental results, the lowest N2O concentration was found to be in the B5 diesel/biodiesel blend. Also, formaldehyde and methane compounds were detected qualitatively, indicating the possible presence of these chemicals in the combustion of diesel/biodiesel blends.