In this paper, the effects of external supercharger application on in-cylinder combustion, performance parameters, fuel efficiency and environmental-economic indicators are discussed together regarding a hydrogen-fueled spark ignition engine operating under a lean mixture. The engine was operated at an engine speed of 1600 rpm, under four different boosting pressures (between 10 kPa and 40 kPa), by optimized ignition timing and being compared to a normally aspirated condition. Hydrogen was injected at five bars into the inlet-air. The results show that the indicated mean effective pressure and thermal efficiency increased by 38.9% and 14.2%, respectively, with a 40 kPa boosting pressure under an optimized ignition timing condition according to the normally aspirated engine, and that the cyclic variation decreased by 15.5%. In addition, under 40 kPa boosting pressure, NOx emissions increased by 45.2% and its environmental-social cost increased by 21.8%, while specific fuel consumption and fuel cost were reduced by approximately 18.5%. (C) 2021 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.