To demonstrate the intensive thinning effect on the coastal forest by extra-high density planting, survival and radial growth of trees were investigated for a 16-year-old Quercus dentata stand by setting up 30%-thinned-, 60%-thinned-and control plots. The plots were censused every 3 years for consecutive 12 years. Radial growth of 30%-thinned plot was slightly larger than that of control plot only in 2004-2007 period. Greater radial growth was observed in 60%-thinned plot just after thinning treatment for consecutive 9 year. Gini coefficient of 30%-thinned plot achieved the same level with control plot, whereas the coefficient of 60%-thinned plot was always lower than control plot. Canopy layer closed during 6 years after thinning in both thinned plots. Our result suggests that 30% thinning has little effects on the improvement of radial growth and furthermore intensive thinning has to be necessary for the density control of the coastal forest by extra-high density planting

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