Proteins and peptides offer high therapeutic specificity but face challenges like enzymatic degradation and low bioavailability. Cellulose-based carriers provide stability. This chapter explores cellulose-based drug delivery systems, their mechanisms of drug loading and release, and their applications in oral, injectable, transdermal, and mucosal delivery. Cellulose derivatives protect proteins, enable controlled release via diffusion, pH sensitivity, and enzyme-triggered degradation, and support advanced delivery strategies like stimuli-responsive materials and 3D-printed scaffolds. Cellulose-based systems enhance protein and peptide drug delivery but require further research on scalability, regulatory approval, and stability for clinical applications.