To investigate the mass absorption efficiency (MAE) of elemental carbon (EC) at Chengdu in China’s Sichuan Basin, daily PM2.5 filter samples were collected during the typical month for each season in 2011. PM2.5 samples were subject to chemical analysis for water-soluble inorganic ions, organic carbon and EC, as well as biomass burning organic tracer (i.e., levoglucosan). Additionally, PM2.5 samples were further conducted for aerosol absorption coefficient (bap) measurement at the wavelengths of 370 and 880 nm. To evaluate the seasonal variations of MAEs of EC, linear regression analyses were applied to EC (determined by thermal method), black carbon (BC, determined by optical method) and bap for four seasons. The average BC concentration was 10 µg m−3 when using the manufacturer’s recommended value (16.6 m2 g−1 at the wavelength of 880 nm), which was 1.4 times the mean EC concentration. The MAE of EC at 880 nm was estimated to be 6.1 m2 g−1 in autumn, which was evidently lower than 6.7–6.9 m2 g−1 in other seasons. The higher MAE in other seasons was likely due to more effective light absorption by internally mixed EC with both transparent coatings (e.g., sulfate and nitrate) and organic matters coatings.