The concentration and speciation of ambient volatile organic compounds (VOCs) in Shanghai downtown and suburban areas were analyzed and measured by using online gas chromatography with flame ionization detection systems (GC-FID) during the spring period (from Mar. 1st to Mar. 31st, 2013) and 55 kinds of VOCs were detected. Maximum ozone formation potential (PhiOFP) and Fractional aerosol coefficients (FAC) were also used to estimate the formation potential of ozone (O3) and secondary organic aerosols (SOA). The results showed that the average concentrations of VOCs were respectively 33.9 x 10(-9) and 20.2 x 10(-9) in the downtown and suburban of shanghai. The main components were alkanes (14.7 x 10(-9)), aromatics (7.7 x 10(-9)) and alkenes (9.3 x 10(-9)) in the downtown; and the main components were alkanes (4.3 x 10(-9)), aromatics (13.9 x 10(-9)) and alkenes (1.8 x 10(-9)) in the suburban. Furthermore, PhiOFP (in the downtown) was 0.58 times of the PhiOFP (in the suburban), while PhiOFP (alkanes) and PhiOFP (alkenes) were 2.2 and 2.1 times in the downtown than suburban, but aromatics was only 0.34 times in the downtown than suburban. Fractional aerosol coefficients (FAC) were also used to estimate the potential formation of secondary organic aerosols (SOA) and the SOA concentration values in the downtown and suburban were 2.04 and 4.04 microg x m(-3), respectively. SOA formations from aromatics and alkanes in the downtown contributed 13.2% and 86. 8% and in the suburban contributed 2.7% and 97.3% to the total SOA formation potential. Aromatics and high-C alkanes were the main components that contributed to the SOA formations in both downtown and suburban of Shanghai in spring.