Polymorphisms of 4-octyloxy-4'cyano-biphenyl was studied by differential scanning calorimetry and time-resolved small angle X-ray scattering. The X-ray scattering identified a new phase and indicated that the crystalline structure of the needle form was different from those reported in literatures. Upon heating, parallel transformations of the needle form into a stable crystal and into smectic phase were observed by the time-resolved scattering, while transformation of the new phase into smectic phase was found absent at low temperatures and the parallel transformations of the new phase into the stable crystal and into smectic phase occurred only at higher temperatures.