To provide a process for preparing polyolefin resin pre-expanded particles which enables to prepare pre-expanded particles having lower fluctuation in expansion ratios. Polyolefin resin pre-expanded particles are prepared by a process comprising steps of dispersing polyolefin resin particles into an aqueous dispersion medium in an autoclave; heating the resin particles to temperature of at least the softening point of the polyolefin resin and pressuring the same; releasing said resin particles from the autoclave through a release port into an atmosphere of lower pressure than the inner pressure of the autoclave; thereby pre-expanding the resin particles, wherein at the releasing step, the resulting pre-expanded particles are contacted with gas of at least 60° C. and collided with a collision board or a container wall disposed at a distance of 5 mm