The crystallization of poly(3-hydroxybutyrate) (PHB) thin films was observed in situ by ATR (attenuated total reflection)-PTIR．The PHB films with different thickness were prepared by means of spin-coating on Al substrates

and then the isothermal crystallization of the PHB films at 200℃ was investigated in situ by ATR-FTIR The results revealed that the crystallization kinetics of PHB films was affected obviously by the film thickness．A reduction in the erystallinity as well as in the rate of crystallization was found with decreasing the film thickness．because the crystallization occurred under constrained geometry conditions．In addition

the effect of film thickness on the orientation of the molecules of the PHB crystals in the films was investigated by polarized ATR-FTIR．The results imply a preferred orientation of the polymer chain axis in the crystals along the surface-normal direction of the flints．The thinner the film thickness

the more the preferred crystalline chain orientation perpendicular to the film surface is.