A cellulose-based sodium alginate/iron hydroxide (C/SA/Fe) composite hydrogel was fabricated by using epichlorohydrin as cross-linking agent as an effective adsorbent for dye. The physicochemical structure of the C/SA/Fe hydrogel was characterized by SEM, FTIR, XRD and TG. The adsorption performance for the removal of methylene blue (MB) was investigated. In addition, the selective adsorption of cationic dye was also studied. The FTIR analysis revealed that the Fe(OH) colloidal particles were successfully combined in the cellulose/sodium alginate hydrogel. The modified hydrogel had better adsorption performance, and the maximum adsorption capacity of C/SA/Fe0.5 for MB was 105.93 mg/g according to the fitting results of adsorption isotherm. The kinetic study showed that the adsorption of MB onto C/SA/Fe was more consistent with the pseudo-second-order model, and was dominated by chemisorption mechanism such as ion exchange or electron sharing. The adsorption data fits well with the Langmuir model. Thermodynamics analysis showed that the MB adsorption by C/SA/Fe was exothermic, spontaneous, favorable and feasible. After five adsorption-desorption cycles, the adsorption capacity was almost unchanged. So, the C/SA/Fe hydrogel is a potential material in the field of the recovery of agricultural by-products or other bio-based cellulose, or environmental protection, etc.