In this study, a naturally available crab shell chitosan of low molecular weight (20 kDa) has been used as adsorbent to evaluate the pollution load in vegetable oil mill effluent. A series of batch experiment was conducted by varying chitosan dosage (100–400 mg), pH (2–9), stirring time (15–90) min and agitation speed (25–150 rpm) to study their effects on adsorption and flocculation processes. The parameters considered for adsorption study are chemical oxygen demand, total suspended solids, electrical conductivity and turbidity. The maximum reduction in chemical oxygen demand, total suspended solids, electrical conductivity and turbidity is 74, 70, 56 and 92 % , respectively. The observed experimental result showed that crab shell chitosan could able to reduce significantly the chemical oxygen demand, turbidity, electrical conductivity and suspended matter. The optimum conditions were estimated as 400 mg/l chitosan, pH 4 and 45 min of mixing time with mixing speed of 50 rpm. Chitosan showed very good pollution removal efficiency and can be used for the effective treatment of vegetable oil mill effluent.