Crystalline cellulose nanofibril (CNF) was isolated from cotton linter pulp using an acid hydrolysis method and used as a filler to reinforce sodium carboxymethyl cellulose (CMC) film. The CNF was in rod shape with the diameter of 23-38 nm and the length of 125-217 nm and crystallinity index (CI) was 0.89. The effect of CNF concentration (1, 3, 5, and 10 wt% based on CMC) on the optical, morphological, mechanical, water vapor barrier, surface hydrophobicity, and thermal properties of the nanocomposites were studied. The CNF was evenly distributed in the polymer matrix to form smooth and flexible films indicating the CNF is highly compatible with the CMC. The tensile strength (TS) and elastic modulus (EM) of CMC film increased by 23% and 27%, respectively, while the elongation (E) decreased by 28% with 5 wt% of CNF inclusion. The WVP of CMC film decreased at low content of CNF, and increased with increase in CNF content, then decreased but to the same level of the control CMC film with the inclusion of 10 wt% of CNF. Transparency of CMC film decreased slightly from 87.7% to 86.2% with 5 wt% of CNF. The CMC/CNF composite films have a high potential to be used as an edible coating or packaging films for the extension of shelf life of fresh and minimally processed fruits and vegetables.