A novel phenomenon called the photoelastic effect had been observed in ZnO nanorods, along with a number of intriguing anomalies. With increasing excitation power, it was found that the A 1 (LO) phonon exhibited a red-shift in frequency, on top of a blue-shift in the photoluminescence (PL) peak energy. In addition, the temperature-dependent photoluminescence spectra behaved quite differently under high and low excitation power. All our results can be accounted for by the photoelastic effect, in which the built-in surface electric field was screened by photoexcited electrons and holes. Through the converse piezoelectric effect, the internal strain was therefore altered. Our results make possible a new thrust for manipulating the physical properties of ZnO nanorods, and should prove very useful in the application of optoelectric devices.