Using two optical techniques, we have studied the hot electron-optical phonon interactions in GaAs/AlxGa1-xAs multiple quantum wells. Raman scattering measurements at 15 K are presented for the Al composition of x = 0.3, 0.5, 0.7 and 1.0. The GaAs-like and AlAs-like phonon frequencies of the first-order modes are also measured as a function of Al compositions. The optical phonon energies emitted by the photoexcited electrons in quantum wells are determined by using hot electron-neutral acceptor luminescence techniques. It is shown that the relaxation of hot electrons in the quantum wells is dominated by the GaAs LO phonon emission for small x, but by AlAs-like LO phonons for larger Al composition.