Novel cellulose acetate (CA) nanofibers incorporated with hormone progesterone (P-4) were prepared by electrospinning and its potential as a controlled release system for medicine and veterinary was evaluated by controlled release essay. The morphology, thermal behavior, and structure of P-4-loaded CA nanofibers were characterized by scanning electron microscopy, differential scanning calorimetry, and Fourier-transform infrared spectroscopy. The analyses revealed that the incorporation of P-4 increased nanofibers' diameter from around 340 to 892 nm to 8% w/w P-4-loaded CA nanofibers. Furthermore, P-4 has demonstrated high interaction with CA affecting its crystalline structure, since pure CA nanofibers presented 67.23% of crystallinity while P-4-loaded CA nanofibers where amorphous. Ultimately, the drug release essay demonstrated a two-stage profile, and regarding release kinetics, the samples evidenced a diffusion mechanism depending on P-4 concentration in the nanofiber.