A process for preparing polyester pellets which involves blending polyethylene terephthalate and polyethylene isophthalate copolymer before solid state polymerization, the polyethylene isophthalate copolymer being composed of dicarboxylic acid constituent units derived from dicarboxylic acids containing terephthalic acid and isophthalic acid and diol constituent units derived from diols containing ethylene glycol and 1,3-bis(2-hydroxyethoxy)benzene, palletizing the blend and crystallizing the pellets.