We have studied theoretically the low-field electron transport in a free-standing quantum well where the deformation potential scattering of electrons by acoustic phonons is the major mechanism of the electron relaxation. The quantization of acoustic phonons, their multisubband spectrum, and the exact form of the dilatational acoustic modes are taken into account. We have numerically solved the kinetic equation for electrons in the low electric field limit. At low lattice temperature the obtained electron distribution function has several peaks associated with scattering by different dilatational phonons. The electron mobility has temperature dependence similar to that described by the Bloch-Grüneisen formula, however we have obtained T −3 dependence of mobility in the low temperature region.