Electron-optical phonon interactions in ultrathin GaAs-AlAs multiple quantum well structures have been studied by using picosecond time-resolved Raman spectroscopy. The authors experimental results have shown that the electrons primarily relax through the emission of interface optical phonons and that the electrons interact not only with GaAs-like interface phonons but also with AlAs-like interface phonons. The interaction strength of electrons with AlAs-like interface phonons has been shown to be much stronger than that of electrons with GaAs-like interface phonons for ultrathin GaAs quantum wells. The strength of electron-AlAs-like interface phonon interaction has been demonstrated to decrease very rapidly as the thickness of the GaAs well increases.