This study identified the relationships between CO_2 emissions from passenger transport and its driving factors by taking Shanghai as an example. The Logarithmic Mean Divisia Index (LMDI) technique was used to disassemble the total passenger transport CO_2 growth into five driving factors: economic activity, population, modal share, passenger transport intensity and passenger transport CO_2 emission factor. The study found that: (1) In 2009, the passenger transport CO_2 emissions in Shanghai increased by 2.59 times against that of 2000; (2) The increased economic activity was the main factor driving passenger transport CO_2 emissions growth from 2000 to 2009 that accounted for 75% of the total passenger transport CO_2 emissions growth in Shanghai; (3) The effects of modal share change and population growth were relatively small but not trivial; (4) The inhibitory effects of passenger transport CO_2 emissions growth were 90% from the improvement of passenger transport intensity, and 10% from the changes of passenger transport CO_2 emission factor. However, these effects were too small to offset the whole increase.