Omeprazole (OME)-loaded cellulose acetate phthalate nanoparticles (CAP NPs) are prepared by the use of microfluidic (MF) nanoprecipitation method for antiulcer evaluations. First, it is found that the samples synthesized by MF have smaller size (~65 nm) with lower polydispersity index (0.09) and higher surface charge (-43 ± 4.23 mV) compared to those obtained via bulk method (BM). (327 characters)