Measurement of 228Ra activities in the upper 300 m water column was conducted at two stations in the South China Sea using an MnO2-fiber extraction/b-counting technique of 228Ac. Results showed that 228Ra activities ranged from 0.38 to 3.60 Bq·m-3. The vertical profiles of 228Ra at the time-series station favored a steady state assumption. Based on a one-dimensional steady state model, 228Ra-nitrate coupled approach was applied to stations NS97-43, NS99-53 (T1), NS99-53 (T2). New production thus quantified were 4.4, 5.1 and 5.7 mmolC·m-2·d-1, respectively. f ratios in the South China Sea were estimated from the derived new production and the documented primary productivity in the regime, to be 0.12-0.15.