Biosorption of acidic dyes using the live fern Azolla filliculoides was studied in a discontinuous system. Dye parameters, dye initial concentration and contact time were studied in temperature range of 25-30 ?C and pH=7. It was shown that increasing the 23initial concentration of dye and its contact time resulted in decreasing the dye taking quantity by the absorbent. Also, type of dye has an effective role in the process. The highest dye taking capacity was reported in the concentration of 15 mg/L that was 64.52%, 37.53%, and 32.98% for acidic red 14, blue 25, and yellow 17 dyes respectively. Adsorption isotherm models of Langmuir, Freundlich, Dubinin- Radushkovich, and Temkin were analyzed in different concentrations. Adsorption kinetic data were considered by kinetic models of pseudo-first-order and pseudo-second-order.