We present online monitoring of nanowires growth within a microfluidic chamber. This achievement is introduced for the first time thanks to simple and noninvasive real-time optical method, where the results were confirmed later by scanning electron microscopy (SEM). Nanowire length and diameter could be monitored versus growth time thanks to remote optical measurement. In this work, we also report kinetics study and online monitoring of in-situ growth of Zinc-Oxide nanowires (ZnO-NWs) within a microfluidic chamber showing the impact of different growth parameters on the NWs characteristics. It appeared that growth within a microfluidic reactor provides 4-times faster growth rate compared to macroscopic growth due to the confined environment of the chemical reaction. It also appears that varying the flow rate has more influence on the NWs diameter rather than the NWs length.