This study was the first to investigate pollution characteristics of atmospheric carbonyls in one haze event (July 17–22, 2012) in Nanning, south China. It was found that (1) acetaldehyde (29.74 ± 6.06 µg m–3), formaldehyde (11.20 ± 1.72 µg m–3), and acetone (9.18 ± 11.22 µg m–3) were the most abundant in haze days, (2) concentrations and O3 formation potentials of ambient carbonyls in haze days were significantly higher than those on normal days, and (3) visibility and wind speed in haze days were lower than those on normal days, indicating that haze days represented favorable pollution conditions for carbonyls. Diurnal variations of ambient carbonyls in haze days showed a pattern of two peaks occurring in two traffic rush-hour periods due to positive traffic emissions. Average concentration ratio of formaldehyde/acetaldehyde (C1/C2) in haze days (0.39 ± 0.10) was slightly lower than that (0.87 ± 0.23) on normal days, and the ratios in two traffic rush-hour periods were close to those in non rush-hour periods, likely implying that traffic emissions might not be a major source for ambient carbonyls. Correlation among formaldehyde, acetaldehyde, acetone, and total carbonyls was good (R2 = 0.49–0.85) in haze days and excellent (R2 = 0.80–0.98) on normal days, indicating that the sources of ambient carbonyls in haze days were more complex compared to normal days.