Polymer systems, in the form of crosslinking networks, have been widely used in biomedicine. However, they are a challenge mainly due to the impact of their physicochemical properties on release kinetics of drugs. Ketoprofen is an analgesic anti‐inflammatory drug with short half‐life (<2 h) and quickly eliminated by the body. Topical administration of ketoprofen can reduce pain, accelerate the wound healing process, and minimize the risk of systemic side effects. Therefore, the aim was to synthesize, characterize, and evaluate a novel ketoprofen polymer system in the form of a semi‐interpenetrated network of poly(ethylene glycol)‐chitosan. The pore size studied by small‐angle X‐ray scattering showed the presence of nanoscale pores, 13.7 nm (dry state) and 26.18 nm (swollen form). The maximum swelling was 420 ± 45% at 24 h. Finally, the encapsulated ketoprofen (6.5%) was released at a constant concentration (0.12 ± 0.03 mg/mL, 8 h) and half of the doses up to 24 h. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018, 135, 46644.