The compatibility of poly (e-caprolactone) (PCL) with poly (styrene-co-acrylonitrile) (SAN) has been investigated using DSC and IR methods. It is shown that the mixture is compatible based on the glass transition temperature measurement. With the increasing concentration of SAN

the melting points of a semicrystalline polymer PCL depress in the PCL/SAN blends. By means of Flory-Huggins equation

the interaction parameter (x23) between these two macromolecules has been evaluated from the melting point depression. The shift and the broadening of the IR absorption hand of carbonyl group indicate that there exizts some spe-cial interaction between ester group in PCL and a-hydrogen in acrylonitrile units of SAN. This interaction results in the compatibility of PCL/SAN blends.