The dynamic properties of light propagation in AlGaN/GaN-based multiple-quantum-well waveguides have been investigated by time-resolved photoluminescence (PL) spectroscopy. The waveguides were patterned with a fixed width of 0.5 μm and length 500 μm using electron-beam lithography and inductively coupled plasma dry etching. Our results reveal a remarkable decrease in the PL intensity as well as an increase in time delay of the temporal response as the location of the laser excitation spot on the waveguide is varied. These results can be understood in terms of polariton propagation in the waveguides. From the time delay of the temporal response, it has been determined that the speed of generated polaritons, with energy corresponding to the well transitions in the waveguides, is approximately (1.26±0.16) × 107 m/s. The implications of these results to waveguiding in optical devices based on the group III-nitride semiconductors are discussed.