The purpose of this study were to investigate the effects of defoliation on chromium treatment ability of vetiver grass (Vetiveria zizanioides (Linn.) Nash) in sub-surface flow constructed wetland. This study had two period that preliminary study and pilot scale constructed wetland study. Preliminary study the effects of defoliation in three concentration wastewaters that 100% chromium wastewater, 50% chromium wastewater and 25% chromium wastewater. The study results showed that the first order equation which emphasizes on k value. The k value is explaining the rate of heavy metal uptake. Analysis of chromium in stream part’s k are 0.0024 and root part’s k are 0.0077. The growth ability: dry weight and height during the experiment period, it was found that growth of both defoliate and non-defoliate experiments were affected by three wastewater concentration (p>0.05). The dry w eight of 25 % v/v wastewater concentration was higher than another wastewater concentration, was 29.95 g, and height of 100% v/v wastewater concentration was higher than another wastewater concentration, was 82.5 cm. But the height increase rate in defoliate experiments were higher than non-defoliate experiments, The higher height increase rate was 25% v/v wastewater concentration (45.5 cm/60 days) Pilot scale constructed wetland study, The efficiency of constructed wetlands to remove chromium in chromium wastewater was studied with vetiver geass on 25% chromium wastewater, Three pilot scale constructed wetlands were built, in which 2 units were used for defoliated effects study and the rest w ere used as the controls The best efficiency was found in vetiver which defoliated at 60 day after start experiment w ere 99.864% respectively. And the lowest efficiency was found in control unit, 99.698% accumulation of chromium in soil and plant were also studied and tended to increases with passage of time. The highest of chromium in soil was found in control experimental, was 33.29 mg / kg soil dry weight. The maximum concentration of chromium in roots were found on non-defoliate vetiver grass w ere 54.43 mg C r / kg at the end of experiment. Mass balance showed that more than 86 % of total chromium was sedimented in to soil