Hydrogels are hydrophilic polymeric networks that are able to absorb huge amount of water. Their applications in industrial and environmental fields are increasingly interested due to their special characteristics and potentials. Hydrogels based on natural polymers like starch, due to their biocompability, biodegradability and abundant sources, are preferred to synthetic ones. Chitin is one of the most abundant biopolymers in nature that has been used recently in synthesis of composites as filler. The aim of this thesis is to extract and characterize chitin nanofibers from Rhizopus oryzae and then add nanofibers to hydrogel based on carboxymethyl-starch and consequently evaluate swelling capacity and heavy metal uptake potentials of hydrogel. In first part, chitin nanofibers was prepared through a chemical-mechanical method. Through the first step of chemical process, alkali insoluble materials (AIM) contains phosphate, chitosan and chitin was obtained by alkali treatment and separation of lipids, proteins and base soluble carbohydrates of cell wall of fungi. In the next step, phosphate was removed from AIM by dilute sulfuric acid and reached to 0.04 g/g AIM. Chitosan was eliminated by sulfuric acid (1% V/V) at 121 o C and chitin fibers (0.95 g/g AIM) was extracted. FTIR spectroscopy indicated the removal of alkali soluble materials, phosphate and chitosan. FTIR data of extracted chitin was in agreement with the results of similar researches. Chitin nanofibers were prepared by ultrasonication. Diameter of chitin fibers before and after ultrasonication were estimated, respectively, 3.8 µm and 49.5 nm by scanning electron microscopy. Furthermore, diameter distribution of chitin fibers after mechanical treatment showed that more than 80% of nanofibers had diameter less than 60 nm. Crystallinity index of nanofibers was assessed 70% by using XRD. In second part of the project, carboxymethyl-starch (CMS) was synthesized and characterized. Carboxymethylation reaction was performed in the presence of isopropanol, sodium hydroxide and monochloroacetic acid. Degree of substitution of carboxymethyl groups was estimated 1.7 using inductively coupled plasma-optic emission spectra (ICP-OES). FTIR data and SEM images confirmed carboxymethylation reaction. Hydrogel was prepared throughout crosslinking of CMS using adipic acid (AA) as crosslinker. Effect of synthesis temperature and AA/ anhydroglucosidic unit (AGU) molar ratio on swelling capacity and metal uptake of hydrogels were investigated. Swelling capacity was obtained 62 g/g dry hydrogel at synthesis temperature of 200 o C and AA/AGU=0.04. In order to enhance swelling capacity and metal uptake of hydrogel, different amounts of chitin nanofibers (3, 5, 7, and 10 % W/W CMS) were added to hydrogel. Maximum swelling of 76 g/g dry hydrogel was obtained for hydrogel reinforced by 5 % W/W nanofiber. Atomic absorption spectrophotometry analysis demonstrates the removal of 77.6%, 85.7% and 82% of Cu, Pb and Cd cations, respectively, from initial concentration of 100 mg/L aqueous solution. However, more than 90% removal of metals were obtained by hydrogel reinforced by 5% nanofiber. Morphology of hydrogels was evaluated by FE-SEM. Keywords: Rhizopus oryzae, chitin nanofiber, carboxymethyl starch, Hydrogel, degree of substitution, crosslinker.