In0.22Ga0.78N/In0.06Ga0.94N multiple quantum well (MQW) microdisks 6.0 μm in diameter have been fabricated by photolithography and ion beam etching. Photoluminescence (PL) spectroscopy has been employed to study the optical transitions in these microdisks as well as in the original MQW structures prior to microdisk formation. With respect to the original MQWs, a blueshift in the PL peak position, enhancement of the PL intensity, and narrowing of the PL linewidth were observed at 10 K in the microdisks. These observations can be understood mainly in terms of a reduction of piezoelectric field strength due to partial strain relief in the microdisks. The magnitude the piezoelectric field reduction was estimated to be around 0.27 MV/cm, which is of the same order as the previously reported value of the piezoelectric field in similar MQW structures.