Abstract: A highly transparent carboxymethyl cellulose (CMC)/cellulose fiber composite film based on cellulose fibers and CMC was rapidly prepared by a combination of paper making method and impregnation, aiming to replace current rigid, non-biodegradable substrates for electronic devices. The optical transmittance of composite films as function of the mass ratio of CMC to northern wood fibers and the influence of the CMC molecular weight on the mechanical properties were investigated.The effect of fiber species (northern wood fiber, eucalyptus wood fiber, manila hemp fiber, bagasse fiber) on the mechanical properties of highly transparent CMC/cellulose fiber composite films was also studied. The results show that the CMC/northern wood fiber composite film exhibits a light transmittance of 90%, a tensile strength of 111 MPa, and a folding endurance up to 2 526 times when the mass ratio of CMC (molecular weight:700 000)to softwood fibers is 7:3. This biodegradable, mechanically flexible, strong, and highly transparent CMC/cellulose fiber composite film shows the potential to be used in the fabrication of next generation flexible and green electronic devices as a substrate to maintain the sustainability of human's society.