The key advantage of microfluidic technology in chemical processing is the high interfacial area, which is especially important in multiphase reactions. Multiphase reactions such as transesterification of vegetable oil and methanol to produce biodiesel are largely dependent on the interfacial area for better mass transfer. However, little attention has been given to the hydrodynamic factor, which affects the interfacial area in the microchannel. In this study, the interfacial area from the droplet flow regime was studied by varying three parameters: Methanol to oil ratio (M/O), total flow rate (QTotal), and catalyst concentration. The droplet flow was created by a cross-junction channel and photos were made to measure the size of the droplets with the help of a microscope. The maximum M/O ratio (23) and the lowest flow rate (10 μL/min) exhibited the highest interfacial area, where increasing the M/O by 67 could increase the interfacial area by 23. By varying the KOH catalyst concentration, the change in the interfacial area was very small, thus having the lowest impact on the interfacial area of the droplet. Further analysis must be performed to investigate the impact of interfacial area and mass transfer coefficient on reaction performance in producing the highest yield of biodiesel in a microchannel reactor. © 2019 Published by ITB Journal Publisher.