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We report a reflectance difference spectroscopy ͑RDS͒ study of the optical anisotropy of GaAs:͑001͒ surface quantum wells consisting of a thin GaAs layer ͑3-30 nm thick͒ embedded between an arsenic reconstructed surface and an AlAs barrier. The RDS spectra display anisotropic contributions from the free surface and from the GaAs/AlAs interface. By comparing RDS spectra for the c(4ϫ4) and (2ϫ4) surface reconstructions, we separate these two contributions, and demonstrate that the anisotropy around the E 1 and E 1 ϩ⌬ 1 transitions comprises a component originating from modifications of bulk states near the surface. The latter is attributed to anisotropic strains induced by the surface reconstruction. The experimental data are well described by a model for the RDS response of the multilayer structures, which also takes into account the blue energy shifts and the changes in oscillator strength of the E 1 and E 1 ϩ⌬ 1 transitions induced by quantum-well confinement.