PM aerosols from Jinan (36°256'N, 117°106'E) in the North China Plain region were investigated for water-soluble organic acids (WSOAs, i.e., oxalic acid, formic acid, acetic acid, methanesulfonic acid (MSA), and lactic acid) during 30 December 2016 to 21 February 2017. The average PM concentration was 168.77 μg/m with about 90.74% samples beyond the National Ambient Air Quality (NAAQ) standards (Grade II). The total concentration of the measured WSOAs averaged at 1.34 μg/m, contributing to 0.80% of PM mass. In the observation, acetic acid was the most abundant WSOA, followed by oxalic acid, lactic acid, formic acid, and MSA. During the period, serious haze events frequently happened. The average concentrations of PM and every WSOA species were higher in haze than those in non-haze. The correlations among species suggested that WSOAs in haze had complicated sources and secondary pathways, especially aqueous-phase reactions which played an important role on WSOAs. The concentrations of WSOAs declined in the Spring Festival compared with those in the non-Spring Festival due to holiday effect. Fireworks burning during the Spring Festival had different influences on WSOAs with slight increases for acetic acid and lactic acid. Five source factors were identified by positive matrix factorization (PMF) model for five WSOAs, respectively, and the results revealed that secondary reactions were the main sources of WSOAs in haze.