This letter reports the realization of liquid tunable long-period grating (LPG) using multiphase droplet microfluidics that is integrated onto a microfluidic chip. A stream of plugs is formed by two immiscible liquids and acted as LPG. It provides the tunability in the grating period by tuning the flow rates of the liquids, the refractive index and the index variation of the core layer by using different combinations of liquids. The experimental results show attenuation strength of 0.14 and attenuation bandwidth of 7.6 nm. The chip is promising as a sensor for biochemical applications and a tunable filter for optical measurement.