A method of producing protein nanoparticles from waste chicken feathers by enzymatic hydrolysis followed by ultrasonic treatment is disclosed. The process includes pretreatment of the chicken feathers. Then feather fibers are hydrolyzed enzymatically. The effects of enzyme concentration, hydrolysis time, and substrate concentration on particle mean size are analyzed to optimize the best condition in order to attain the smallest particles by a Box-Behnken Design. A minimum particle size is obtained by using 5 g/l feather and 3.6% enzyme with a hydrolysis time of 243 h. The hydrolyzed particles are then subjected to ultrasonic treatment to produce nanoparticles. The produced protein particles have high potential to be used in nanocomposites and adsorbents.