The effect of alkoxy substitution on the photophysical properties of poly(p-phenylenevinylene) [PPV] was investigated using steady-state and time-resolved photoluminescence, visible and infrared absorption spectroscopies. By substituting the alkoxy group (methoxy or butoxy) into the phenylene ring of PPV, the prolongation of effective conjugation length accompanied by the disappearance of the well-resolved vibronic structure was detected in the absorption spectra. These experimental results were attributable to the electron donating effect and the steric hindrance of the alkoxy substituent. These conjectures were compared with the effect of the alkoxy substitution on the photoluminescence and the Fourier-transform infrared spectra. Also, it was found that, alkoxy substitution slowed down the exciton relaxation process from the lower exciton state to the ground state, and lowered the height of the potential barrier in an excitonic potential well.