Here, microfluidic biosynthesis of Ag nanoparticles (AgNPs) in tubular microreactors in the presence of Cacumen Platycladi (C. Platycladi) extract was studied, focusing on the effect of technical parameters (volumetric flow rate, the concentration of C. Platycladi extract, inlet mixing pattern) and reactor parameters (reactor materials and inner diameter) on the size distribution of AgNPs. Computational fluid dynamics (CFD) was utilized to simulate the profile evolution of velocity, biomass concentration and temperature in the microreactors. It was found that, unlike in traditional bulk reactors, the interfacial effect between the solid surface and bulk solutions in microreactors could not be ignored and had crucial influence on particle size distribution. Results of CFD simulation confirmed that microchannels possessed some unique flow characteristics and various process parameters had specific influences on the size distribution of the AgNPs, which could be explained in terms of their influences on the interfacial effect and flow characteristics. Our work provides useful insight into the influence of process parameters on size distribution of AgNPs in microfluidic biosynthesis. (C) 2012 Elsevier B.V. All rights reserved.