Ring-banded morphology of polymerized cyclic butylene terephthalate (pCBT) accompanied by the synchronous evolution of non-ring-banded patterns was investigated for the first time through the crystallization of pCBT prepared by ring-opening polymerization (ROP) of cyclic butylene terephthalate oligomers (CBT). The result of gel permeation chromatography (GPC) shows that pCBT has a broader molecular weight distribution than commercial poly(butylene terephthalate) (PBT). The polar optical microscope (POM), atomic force microscopy (AFM) and scanning electron microscope (SEM) demonstrate that the ring-banded patterns originate from the lamellae twisting. The radial growth rates, in situ evolution and melting observation from the POM prove that the crystals' melting point in ring-bands is lower than that in non-ring-banded parts. And the crystals in ring-bands are deduced to be constructed by the low molecular weight pCBT fractions. Finally, the possible formation mechanism is discussed.