Amorphous poly(ethylene naphthalate) (PEN) oligomer has been crystallized at room temperature by treating in liquids having solubility parameter, delta, in the range of 15-29 (J.cm(-3))(1/2). It has been observed that the liquids having delta in the range of 18.5-25 are able to crystallize PEN oligomer efficiently. A direct correlation has been observed between delta and crystallite size calculated from WAXS technique.