Background: Polymeric nanomaterials are important for developing drug delivery systems. The control of nanoparticle size, polydispersity, and morphology in these systems are important goals. Therefore, different strategies have been explored depending on the type of materials used. Objective: To prepare biodegradable segmented poly(urea)urethane nanoparticles and to optimize the nanoparticle size and polydispersity using an experimental design methodology. Methods: In this work, a biodegradable segmented poly(urea)urethane (SPUU) was synthesized. This polymer was used for nanoparticle preparation by the nanoprecipitation technique in the context of the experimental design methodology Taguchi L9. SPUU and nanoparticles were characterized using Fourier transformed infrared, proton nuclear magnetic resonance, transmission electron microscopy, scanning electron microscopy, and dynamic light scattering. Results: This methodology produced polymeric nanoparticles with mean sizes in the range of 60 to 220 nm with polydispersity in the range of 0.077 to 0.233. The statistical analysis showed that the SPUU concentration and the stirring speed were the most influential parameters, while temperature, at the studied range, did not show a relevant effect. Conclusion: The analysis of Taguchi’s experimental design resulted in the optimization of parameters determining SPUU-NPs’ size. Nanoparticles from 60 nm of effective diameter were obtained at low polymer concentration and higher stirring speed.