Abstract: Provided is a microfluidic chip for generating a plurality of droplets comprising plural droplet-forming units serially connected together, an inlet for receiving the loading fluid and providing the loading fluid to the plural droplet-forming units, and an outlet for discharging the loading fluid remained after passing through the plural droplet-forming units. Each of the individual droplet-forming unit include an inflow channel, a neck channel, a droplet-forming well and a bypass channel therearound, a restricted flow port element, and an outflow channel, the arrangement of which allows the microfluidic chip to form robust and stable droplets for reliable and flexible drug screening assays using a small sample input size.