To remove an oligomer from fine substantially crystalline α-olefin polymer particles containing the oligomer in an effective concentration without melting the particles.

The temperature of a floor containing α-olefin polymer particles is set at a temperature high enough to evaporate the oligomer from the particles but not enough to cause them to be sticky to such as extent that they are substantially agglomerated and adhere to the wall, etc. The floor is fluidized by passing a gas stream inert to the particles and the oligomer therethrough at a floor-fluidizing velocity under general conditions and the evaporated oligomer is removed from the floor. The particles are kept at this temperature for a time long enough to evaporate a substantial portion of the oligomer. According to this method, the content of the oligomer and the chain length can be controlled by adjusting the floor temperature and the residence time.