BACKGROUND: Biological synthesis of platinum nanoparticles (PtNPs) with Cacumen platycladi (C. platycladi) in a microfluidic chip and numerical simulation of formation processeswere studied. The effect of volumetric flowrate on PtNPs` size distribution was investigated in detail not only by experimental methods but also by means of numerical simulation. Computational fluid dynamics (CFD) and a population balance model (PBM) combined with reactive kinetics were employed to simulate PtNPs` formation and to calculate the particle size distributions (PSD). RESULTS: The experimental results confirmed the validity of the model and its practicality in predicting the formation of PtNPs and PSD evolution in the microfluidic chip. In addition, the numerical simulation results also tested and verified the accuracy of the results and conclusions acquired fromthe experiment. CONCLUSION: It is concluded that PSDwas influenced not only bymixing efficiency but also by residence time in themicrofluidic chip, and that the two factors were determined by volumetric flow rate. There is a specific volumetric flow rate to achieve equilibrium (optimal mixing and residence time) that results in the average particle size reaching its maximum value. This work provides useful insight into the microfluidic biological synthesis of PtNPs and the influence of volumetric flow rate on size distribution in a microfluidic chip. (C) 2017 Society of Chemical Industry