Distributions of radium isotopes were investigated in the Pearl River Estuary (PRE) to quantify submarine groundwater discharge (SGD).   The water in PRE is mainly a mixture of river water, ocean water and groundwater. Based on conservation of salinity and 226Ra, we set up a three-endmember mixing model to solve for the fraction of the river water, ocean water, and the groundwater. River water contributed 78±13% of the water mass in PRE, while the ocean water accounted for 19±13% and the groundwater accounted for 3±2%. Using a tidal prism model the flushing time was estimated to be 7.1±0.9 days. Based on the mass balance of 226Ra and 228Ra and the assumption of steady state, the flux of SGD was estimated to be 0.83±0.63-1.07±0.83×108 m3 d-1, which is equivalent to 16-20% of the concurrent Pearl River discharge. The net solute flux via SGD was calculated to be 3.13±2.78×108 mol d-1 for DIC, 1.56±1.96×107 mol d-1 for DOC, 7.35±14.9×104 mol d-1 for soluble reactive phosphorus (SRP), 2.81±2.44×107 mol d-1 for silicate, and 2.67±2.42×107 mol d-1 for dissolved inorganic nitrogen (DIN). The net SGD-associated solute flux accounts for 43% of the estuarine export flux for DIC, 6.69% for SRP, 37% for silicate, and 32% for DIN and is equivalent to 58% of the riverine flux for DIC, 6.99% for SRP, 33% for silicate, and 27% for DIN.