Knowledge of the chemical characteristics and sources of organic aerosols (OA) over marine is needed for evaluating their effects on climate change and air quality. Here, a quadrupole aerosol chemical speciation monitor (Q-ACSM) and a single-particle aerosol mass spectrometry (SPAMS) were synchronously employed to investigate the chemical composition, mixing state, and oxidation degree of oxidized organic aerosols (OOA) in PM1 over the East China Sea (ECS) from 3 to 27 June 2017. Both aerosol mass spectrometers demonstrated that a higher oxidation state of OOA in aerosol particles could be generated during marine air mass-dominated periods (MDP) than that generated during land air mass-dominated periods (LDP). Two OOA factors including semi-volatile oxidized organic aerosol (SV-OOA) and low-volatility oxidized organic aerosol (LV-OOA) were distinguished based on Q-ACSM. Fifty-seven percent of the total detected particles with obvious signals of organic markers were identified as oxidized organic carbon (OOC) particles via SPAMS and further divided into lower oxidized organic carbon (LOOC) particles and more oxidized organic carbon (MOOC) particles. All OOC-containing particles were clustered into seven particle subgroups. The EC and K subgroups dominated the LOOC and MOOC particles, respectively, during periods controlled by land air masses, indicating that notable OOC formation was influenced by continental sources. OOA with higher oxygen states were found to dominate near ports. This suggested that OOA chemical characteristics over the ESC are seriously affected by continental, ship, and port emissions, which should be synergistically considered in evaluating their effects on solar radiation transfer and cloud processes.