Abstract: This paper assessed the potential environmental impacts generated in the life cycle of biodiesel which was made from microalgae cultivated in open ponds. The functional unit was 1 MJ diesel product. The results showed that the most prominent impact category in the life cycle of microalgae biodiesel was non-renewable resources depletion potential, and the second one was photochemical ozone creation potential. The total environmental impact indicator in the life cycle of microalgae biodiesel was 4.63×10-4 equivalent persons, decreased by 19.34% than that of fossil diesel, and the life cycle total environmental impact indicator of rapeseed biodiesel was 7.19 times of that of microalgae based biodiesel. The contributions of stages of microalgae cultivation and biodiesel conversion to the life cycle total environmental impact indicator of microalgae biodiesel were 28.23% and 46.61% respectively. Biodiesel made from microalgae cultivated in open ponds has better environmental performance than fossil diesel and biodiesel made from rapeseed. The essential measure to control the environmental impacts in the life cycle of microalgae biodiesel is to reduce the power consumption in the stages of microalgae cultivation and biodiesel conversion.