We measured the methane concentrations and aerobic methane oxidation rates (MOx) in the seawater of East China Sea and Yellow Sea. Seawater samples were collected onboard "Dong Fang Hong 3" in April 2021 using a rosette system equipped with 24-liter Niskin bottles and a Seabird 911 CTD. Methane concentrations were measured using a purge-and-trap preconcentration method with a gas chromatography (Shimadzu GC-2014B) with a flame ionization detector. The rate constants of MOx and MOx rates were determined using a radiotracer approach through quantifying the conversion of added 3H-methane tracer to the oxidation product 3H-H2O.