To better understand the characteristics, origins and secondary formation and transformation pathways of water-soluble organic aerosols in the Tianjin region, North China, we studied dicarboxylic acids, oxocarboxylic acids and α-dicarbonyls in fine aerosols (PM2.5) collected at an urban (Nankai District, ND; n = 121) and a suburban (Haihe Education Park, HEP; n = 40) sites in Tianjin from 5 July 2018 to 4 July 2019. Concentrations of diacids and related compounds were measured using a capillary gas chromatography (GC; Agilent 7890B). Peak identification was carried out with reference to authentic standards retention time measured by GC-FID and mass spectra performed using a GC-mass spectrometry (GC-MS) system. During the campaign, hourly averaged air quality data such as the oxidants (O3 and NO2) and SO2 in Tianjin were recorded from China National Environmental Monitoring Centre (http://www.cnemc.cn/), and the meteorological data were downloaded at https://darksky.net/forecast/39.1236,117.1981/si12/en and/or monitored by weather station (CR1000X, Campbell Scientific Ltd. Company) installed beside the sampler at both the sampling sites. Based on seasonal variations in their molecular distributions and linear relations among the selected species, and with marker ions, gaseous pollutants and meteorological parameters, we found that the diacids and related compounds were mainly derived from anthropogenic activities such as fossil fuel including coal combustion and biomass burning, and subsequent secondary processes, preferably in gaseous- and aqueous-phases in warm and cold periods, respectively, in Tianjin, North China.