In vitro drug release mechanism of core/shell nanofibers of poly(methyl methacrylate)(PMMA)-nylon6 fabricated through coaxial electrospinning containing different concentrations of ampicillin was investigated. Scanning electron microscopy (SEM), transmission electron microscopy (TEM), Korsmeyer-Peppas equation and Fickian diffusion model were utilized to characterize the system. Antibacterial activity of the designed drug delivery system was investigated against Gram-positive Listeria innocua through optical density (OD) measurement. The system showed sustained drug release through three stages; although the release in stage I followed non-Fickian diffusion, Fickian diffusion was proven to be the release mechanism of stages II and III. A significant decrease in the diffusion coefficient from stage II to stage III was observed, which is believed to be the consequence of crystallization of fibers as a result of long-term incubation in an aqueous solution. Finally, the antibacterial activity of the system was verified by means of optical density (OD) measurements against Gram-positive L innocua. (C) 2013 Elsevier Ltd. All rights reserved.