The ability to control particle size and size distribution of nanoparticles for drug delivery is essential because it impacts on the biodistribution and cellular uptake of nanoparticles. We present a novel microfluidic assisted nanoprecipitation strategy that enables synthesis of surfactant-free curcumin encapsulated poly(lactide-co-glycolide) nanoparticles (Cur-PLGA NP) with adjustable particle diameters (30-70 nm) and narrow particle size distribution (polydispersity index less than 0.2). Our Cur-PLGA NP exhibit excellent colloidal stability and inhibit degradation of curcumin. We further demonstrate the potential of our Cur-PLGA NP as a nanotoxic delivery system for curcumin. Cellular viability assay validates a dose-dependent cytotoxicity of Cur-PLGA NP in leukemia Jurkat cells. In contrast, Cur-PLGA NP does not alter the viability of fibroblast NIH3T3 cells, which suggests that the cytotoxicity of Cur-PLGA NP is specific to cell types. Furthermore, there is no detectable effect by PLGA NP to both leukemia Jurkat cells and fibroblast NIH3T3 cells, highlighting the nontoxic nature of our delivery system. Confocal cell uptake studies indicate that PLGA NP do not alter the cell uptake of curcumin. Our microfluidic assisted approach offers a controlled and effective nanobiomaterials synthesis of drug delivery system for curcumin, which can be extended to different capsule materials for a variety of biomedical applications.