In the last decade, due to environmental challenges and non-renewability of fossil sources, synthetic polymers in many applications have been replaced by biopolymers where the long term-durability is not needed. The thermoplastic starch is wildly used in various domains such as food containers and packing industries. Within the wide family of biopolymers, the starch has the high usage because of its availability, biodegradability, biocompatibility, and ease of chemical modification. Starch is extensively found in seeds, stems, leaves, tubers, and fruits of plants. Starch is a hydrophilic polymer that consist of anhydro-glucose unites linked by ?-D-1, 4-glycosidic bonds. Starch contains of two different main phases of amylose (linear) and amylopectin (non-linear). Biological interactions, post modification, and processing conditions are the most effective parameters in arrangement of these distinct phases. Starch can be converted to thermoplastic starch via incorporation of plasticizers such as water and or polyalcohols. Compare to synthetic polymers, starch has some disadvantages such as high water sensitivity, brittleness, low mechanical properties, and poor barrier properties. To overcome these problems, some solutions such as blending with other biopolymers, chemical modifications, and also reinforceing with nanofillers such as nanoclay and cellulose nanofibers (CNF) have been suggested. Cellulose nanofibers, in addition to biodegradability, biocompatibility, have high crystallinity, high aspect ratio, and low density (compared to glass fibers) that cause noticeable increase in stiffness of matrix In the present study, bio-nanocomposite films were manufactured using thermoplastic starch and cellulose nanofibers. Nanofibers were extracted from rice straw employing a chemo-mechanical method. Chemo–mechanical treatment included: swelling, acid hydrolysis, alkali treatment, bleaching and sonication. A design of experiment was used for acid hydrolysis step to optimize the concentration of acid, ratio of acid to pulp and time of treatment to achieve the highest total crystallinity index. The dimensions and morphology of chemically treated fibers and extracted nanofibers were investigated by scanning electron microscopy and field emission scanning electron microscopy, respectively. The chemical compositions of fibers including cellulose, hemicelluloses, lignin, and silica were determined by different tests. The achieved results showed that the cellulose content was increased around 71% for alkali treated fibers compare to raw materials. Also, it can be noticed that almost all of the silica content of fibers was solubilized in the swelling step. The thermal gravimetric analyses were performed on untreated and bleached fibers. It was demonstrated that the degradation temperature was increased around 19% for purified fibers compare to raw materials. Afterward, bio-nanocomposites were manufactured employing cellulose nanofibers and thermoplastic starch via film casting. In order to study the effect of nanofibers reinforcement on composite properties, mechanical and dynamic mechanical properties, morphology, humidity absorption, and traarency of films were investigated at various nanofibers contents. The yield strength and young modulus of nanocomposites were satisfactorily enhanced compare to pure starch film. The glass transition temperature of films was shifted to higher temperatures by increasing nanofiber contents. The SEM images illustrated that nanofibers were dispersed uniformly in the matrix. The humidity absorption resistance of films revealed significant enhancement until 10 wt% cellulose nanofibers. The traarency of nanocomposites was reduced with respect to pure starch film. Keywords : bio nanocomposites, nellulose nanofibers, ultrasonication, thermoplastic starch, film casting