Light absorption properties of water-soluble organic carbon (WSOC) were investigated in the urban area of Guangzhou. The fine particulate matter (PM₂.₅) and size-segregated samples were collected in September and December of 2014 and January of 2015. The variation of absorption with wavelength of WSOC was characterized by the absorption Angström exponent (AAEabs). The AAE values of WSOC in PM₂.₅ were 3.72 ± 0.41 in autumn and 3.91 ± 0.70 in winter, which were lower than those in Beijing and north America. The mass absorption efficiency (MAE) of WSOC at 365 nm wavelength was 0.52 m² · g⁻¹ in autumn and 0.92 m² · g⁻¹ in winter, exhibiting distinct variations between autumn and winter. In winter, the MAEwsoc values exhibited a decreasing trend with increasing particle size, and all size-segregated MAE(WSOC) values in autumn were lower than those in winter, particularly for the particles < 0.95 µm, suggesting more contribution of the secondary formation to WSOC. Comparing the MAE values of elemental carbon (EC) and WSOC, it could be found that the contribution of WSOC to the light extinction of particles couldn't be ignored when the particles were mainly emitted from primary sources.