Spray drying is an important method used in pharmaceutical product manufacturing for many years. The nano-spray dryer developed in recent years provides ultrafine powders at nanoscale and high product yields. In this study, which was aimed at prolonged release in oral use, nanoparticles-(NPs) were obtained by nanoenglobation of cefaclor monohydrate-(CEF) with Eudragit RS 100-(ERS) with the help of nano-spray drying method. The particle size (PS) of the blank formulation was 186 nrn whereas PSs of CEF containing NPs were between 328 and 389 nm. The average PDI of all NP formulations were below 0.4 and all prepared NPs had a positive ZP value. The encapsulation efficiency values were a range of 78-84 %. In vitro release studies of NPs showed extended-release up to 24 hours after the first 3 hours of burst effect. The results showed that the release kinetics were fitted to the Korsmeyer-Peppas model. As a result, it was found that all pharmaceutical technology analysis results were affected by the solid concentration ratio in the feed dispersion. Antibacterial activity of NP formulations was determined by microdilution method. After minimum inhibitory concentration (MIC) determination, time-dependent activity for NP-2 was investigated by the time-kill method. MIC value for NP-2 was 4-fold lower than MIC value of CEF for Staphylococcus aureus and Escherichia coli. No growth was observed for both bacteria with NP-2 during 18 hours incubation in the time-kill method. As a result, prolonged antibiotic release and long-term antibacterial activity were obtained by NP-2, the optimum formulation of our study.