Hydrotreating processes are important for the production of clean fuels and ultra-clean fuels. However, these processes consume a considerable amount of energy and trigger environmental problems. The production of ultra-clean fuels may lead to increased environmental loads. In this work, environmental impacts of hydrotreating processes for the production of clean fuels are quantified by Eco-indicator 99, which is based on the life cycle analysis. A diesel hydrotreating process is taken as an example to investigate the environmental impacts of the process with various sulfur contents in diesel and feed oil, in which simulations are carried out on the platform of ASPEN Plus. The results indicate that the optimal sulfur content range in diesel is 167.3-191.7 ppm, where the environmental impacts of the diesel hydrotreating process are minimized and the cost of utilities is relatively low. Moreover, the environmental impacts exhibit an approximately linear relationship with the sulfur content in the feed oil. The results also show the decreased sulfur content in the clean fuel does not reduce the environmental impacts of clean fuel production by using the hydrotreating process. Consequently, much more attention should be focused on the environmental impacts of the production process of clean fuel rather than the final product of clean fuel. (C) 2015 Elsevier Ltd. All rights reserved.