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This study aimed to quantitatively estimate and compare the environmental sustainability of docked and dockless bike-sharing promotions. The greenhouse gas (GHG) emission reduction effect and potential of different bike-sharing modes in the five cities of Beijing, Guangzhou, Hangzhou, Nanjing, and Shanghai in China were compared and analyzed using the life-cycle assessment (LCA) approach. The empirical analysis of current data showed that compared with that by the small-scale traditional docked bike-sharing (DBS), the promotion of large-scale dockless bike-sharing (DLBS) has increased the amount of urban green travel; however, it has reduced the operating efficiency of the urban bike-sharing system. On average, the life-cycle mileage of DLBS bikes was only approximately one-third that of DBS bikes, and the corresponding GHG emission intensity of DLBS was approximately twice that of DBS. The GHG emission reduction benefit per kilometer of DLBS trips was lower than that of DBS trips in the same city. In particular, the promotion of DLBS has exerted significant negative effects in Beijing, Shanghai, and Hangzhou. Notably, the environmental sustainability of bike-sharing depends on the utilization of shared bikes. When the life-cycle mileage of the shared-bike was less than 8000 km, DLBS was more environmentally friendly than DBS; otherwise, DBS was more environmentally friendly. Under the current modal shift structures, the maximum GHG emission reduction potential of the DLBS was approximately 25 % lower than that of the DBS. Significant differences in the development status of DBS and DLBS systems in different cities significantly affected their corresponding environmental impacts. Hence, city managers and planners should consider the scale and efficiency of a city's bike-sharing system according to its actual situation and seek an optimal balance point. To ensure complete utilization of the emission reduction potential of bike-sharing, the government and enterprises should strive to shift from car travel to bike-sharing travel and increase the utilization of shared bikes. • Environment friendliness of dockless and docked bike-sharing in Chinese cities was compared. • Environmental impact of bike-sharing showed significant geographical differences. • Dockless mode was less environmentally friendly owing to low operating efficiency. • Increasing bike utilization can significantly improve the sustainability of dockless mode. • The maximum GHG reduction potential of bike-sharing travel could reach 30–40 g CO 2 -eq/km. [ABSTRACT FROM AUTHOR]