The adsorption isotherms were obtained by varying As(III) concentration from 0.2 to 2.0 mg/L at 10 g/L adsorbent dose, mixing time 8 h, pH 4 and mixing speed of 80 rpm when room temperature was 26 1 C. Fig. 3 reveals that the adsorptions of As(III) on coconut fiber adsorbent is concentration dependent. Sorption increases with increase of initial adsorbate concentration. 0.047 mg As(III) was adsorbed per gram of adsorbent at 0.5 mg/L initial concentration and increased to 0.123 mg/g at 2 mg/L As(III) concentration. The increase in sorption with increase of initial As (III) concentration might be due to increased concentration gradient [18,19].