Over the past decade, society’s concern for the state of the environment has increased. Several actions have been taken by governments, non-governmental organizations, public and private environmental and health agencies to limit pollutant emissions. Within this context, the control of vehicle emissions has become increasingly stringent. Emission limits have been substantially reduced, and the role of unregulated emissions is increasing in importance.Ammonia is the third most abundant nitrogen compound in the atmosphere. Ammonia emissions have received special attention due to their contribution to secondary particulate matter production in the forms of ammonium nitrate (NH4NO3) and ammonium sulfate ((NH4)2SO4).The aim of this work was to evaluate the effect of fuel sulfur content on ammonia emissions in a Euro III motorcycle.Tests were conducted on a chassis dynamometer according to the WMTC drive cycle in a Euro lll motorcycle equipped with electronic fuel injection (EFI) and one three-way catalytic converter (TWC). Regulated emissions (CO, HC and NOx) were measured using 7000 series Horiba benches. Unregulated emissions were measured using a SESAM series AVL Fourier Transform Infrared (FTIR) spectrometer. Pre- and post-catalytic converter FTIR measurements were performed. The motorcycle was fueled with A22 gasoline containing 22% anhydrous ethanol and three different sulfur contents (50, 200 and 400ppm).The main finding was that the reduction in the gasoline sulfur content tends to cause an increase in NH3 and CO2 emissions and a reduction in THC, aldehydes and other regulated gases.The catalytic efficiency was improved with fuels containing low sulfur contents, and localized ammonia formation appears to occur inside the catalytic converter. The results showed an increase in ammonia emissions by reducing the sulfur content of 68.601 mg km-1 (S400) to 83.090 mg km-1(S50).