We report on the evolution of the excitonic optical features from two dimensions (2D) to one dimension (1D) in GaAs/AlAs fractional‐layer‐superlattice (FLS) wire structures. We demonstrate for the first time how the excitonic optical properties continuously evolve from 2D to 1D by introducing the FLS lateral compositional modulation in an AlGaAs quantum well. We also present a theory numerically analyzing the optical absorption properties in the FLS wires. Present theory accurately reproduces the experimental results using the AlAs/GaAs FLS wires and clarifies the main optical features associated with excitons in the intermediate quantum‐confinement regime between 1D and 2D. ©1996 American Institute of Physics.