How to account for GHG emissions for public transport is now a key issue for low-carbon city development. This study provides a method to evaluate carbon footprinting for public transport systems in Xiamen city, China across the life cycle. This method, which was based on the life cycle assessment approach including three components - infrastructure, fuels and vehicles - was presented to account the GHG emissions of public transport. The GHG emissions of the two kinds of public transport systems (bus rapid transit [BRT] and normal bus transit [NRT]) in Xiamen City were compared. Results showed that the average carbon emissions of the BRT system was 638.44 gCO2e per person, and that of the NBT system was 2,088.38 gCO2e. If we only took the direct carbon emissions of fuel consumption in the vehicle operation into consideration, the average carbon emissions were, respectively, approximately 149.08 gCO2e per person and 260.84 gCO2e per person by BRT and NBT system. The results indicated that the effects of energy saving from the BRT system are better than NBT system, which is related to the features of the BRT system such as large volume, energy-saving and environment-friendly vehicle type and exclusive right-of way.