Electron-optical phonon scattering rates in ultrathin GaAs-AlAs multiple quantum well structures have been directly measured by using time-resolved Raman spectroscopy on a subpicosecond timescale. We have found that when the GaAs well width increases from 20 to 60 Å, electron-AlAs-like-optical phonon scattering rate decreases by a factor of about 3. The experimental results are explained with theoretical calculations of electron-optical phonon interactions recently carried out by K. Huang and B. Zhu [Phys. Rev. B 38, 13377 (1988)].