Nanopillars with diameters down to 20 nm were fabricated from InGaN/GaN multiple quantum wells (MQWs) by using a nanosphere-SiO2 double mask and inductively coupled plasma (ICP) etching. Clear photoluminescence (PL) signals of the nanopillars were observed at room temperature, and the PL peak energy at 20 K showed a large blueshift of 220 meV compared with that of the original MQWs. The exciton activation energy in the temperature range of 100 ∼ 300 K increased from 33 meV for MQWs to 83 meV for nanopillars. According to the measurements and numerical simulation results, the strain relaxation effect is believed to play a dominant role rather than the quantum confinement effect in determining the emission wavelength of nanopillars. This work also demonstrates a promising method for obtaining III-nitride quantum dots.