We present microphotoluminescence (PL) and micro-Raman measurements with varying the applied electric field in InxGa1-xN/GaN multiple quantum wells (MQWs). The InGaN A1(LO) phonon was found to show a redshift in frequency with the increase of applied electric field. And, a blueshift in PL spectra has been observed when the applied electric field was increased. Quite interestingly, the change in the refractive index was also observed, which was determined accurately from the interference pattern shown in the emission spectra. This finding correlates very well with the blueshift of PL spectra and the redshift of the InGaN A1(LO) phonon. Based on the stress change induced by the compensation between piezoelectric and external fields, our results firmly establish that strong electro-optical and photoelastic effects do exist in InxGa1-xN/GaN MQWs, which is important in the design of optoelectronic devices. © 2003 American Institute of Physics.