This study was conducted to develop economic thresholds for western flower thrips (Frankliniella occidentalis Pergande) on green hot pepper under plastic greenhouse at the National Institute of Agricultural Science and Technology, Suwon, Korea, in 2004. To investigate the relationship between thrips density and damage in fruits, experimental plots with five treatments (0, 4, 16, 48, 96 adults per plot) as initial infestation density were established. The density was monitored using flower counts weekly and yellow sticky trap (8x13cm) semiweekly.  The effect of western flower thrips injury was prominent in the increase of damaged fruits ratio rather than yield loss of fruits. The damaged fruits had lower quality due to the feeding scars on its surface. The ratio of damaged fruits had significant linear relationship with adults or nymphs density in flowers monitored through observation before damage examination (y=0.3219x+1.0792, r²=0.864). It had significant logarithmic relationship with density of adults monitored by yellow sticky traps for four days before damage examination (y=11.9209 log(x)-2.158, r²=0.8306). The economically tolerable percentage of damaged fruits based on control costs and market values of green hot peppers under current greenhouse cultivation was 3.4 to 8.0 %. The economic thresholds for western flower thrips ranged 0.7 to 2.1 adults or nymphs thrips per flower, and 2.3 to 5.7 adults per sticky trap for four days on green hot pepper under greenhouse in Korea.