In this research, the duckweed (Lemna gibba) potential has been investigated spectrophotometrically as an obvious bioagent for the biological decolorization of organic dye Basic Green 4 (BG4). Experiment result showed that L. gibba has a potent ability to extract BG4 from contaminated water. The study showed that for better results the temperature at 25-30 oC and pH 8.0 is considered to be optimum. A significant induction in SOD, GPOD and CAT activity was observed in L. gibba treated with 15 and 30 mg / l BG4, respectively, after 24 hours of biodecolorization process. It was observed during five repeated batch run that L. gibba showed comparable efficiency in dye decolorization. The chlorophyll fluorescence analysis also shows that photosynthetic apparatus of L. gibba is highly tolerant of BG4. The overall results of the observations here demonstrate the duckweed L. gibba can be used as a potent biodegrading organism for BG4.