The purpose of this study was to investigate the characteristics and source apportionment of carbonaceous aerosols in PM10 for the daytime and nighttime during spring and summer over Lanzhou. The samples were collected from 1 April 2015 to 30 August 2015, daytime samples were collected during 08:00 to 20:00 and nighttime samples during 20:00 to 08:00 on the next day, and organic carbon (OC) and elemental carbon (EC) concentrations were measured. The results showed that PM10, OC and EC concentrations were (136.0 +/- 84.3), (12.4 +/- 3.2), (2.3 +/- 0.7) mu g.m(-3) during the daytime, and (196.0 +/- 109.2), (16.0 +/- 5.3), (5.0 +/- 2.1) mu g.m(-3) during the nighttime. The mass concentrations of PM10, OC and EC in the nighttime were higher than those during the daytime. The ratios of secondary organic carbon to total organic carbon were higher in the daytime than nighttime, suggesting that the secondary organic carbon pollution was more serious in the daytime. In sand-dust weather, the concentrations of PM10 and OC were higher than those in non-dust weather, while the EC concentration was close to that in non-dust weather. Secondary organic carbon and total carbon aerosols were higher in sand-dust weather, but the contribution to the PM10 was relatively low. In addition, principal component analysis on the eight carbon fractions of non-dust weather indicated that coal combustion, vehicle exhaust and biomass burning were the major sources for carbonaceous aerosol during the daytime, while coal combustion, dust, diesel exhaust and biomass burning played important roles in the nighttime.