Abstract: Microbially induced calcium carbonate precipitation (MICP) is a novel technique for soil reinforcement based on biomineralization. The MICP regime has not been fully explored due to the complexity of biomineralization process with so many factors affecting nucleation and growth of minerals. Recently, biomineralization evolution could be visually observed at microscale by microfluidic system, whereas the magnification for observation of crystal growth is still limited. In this study, a droplet microfluidic chip was designed to generate oblate droplet cells with 450μm in diameter by adjusting the flow velocities of two immiscible liquids, which can be used for MICP microreactor, i.e., droplet microfluidic system for biomineralization with high precision. With the help of the system, we found that the distribution of bacteria around CaCO3 crystals was almost unchanged with the CaCO3 crystals growing proportionally and the crystal morphology remained the same. Some bacterial cells nearby the crystal were adsorbed on the crystal surface during the crystal growth with no obvious bacterial aggregation around the crystal. In addition, with the help of SEM, some caves on the crystal surface were found to be the sites that bacterial cells were adsorbed. Consequently, the droplet microfluidic system can provide a precise microreactor for biomineralization and an effective method for exploring nucleation regimes in MICP.