Polyesteramide(PEA) was prepared by the polymerization of oligoester(OE) with oligoamide(OA). Oligoester was made by reaction of terephthalic acid(TPA) with ethylene glycol(EG), oligoamide by polymerizaton of 6-aminocaprolc acid. PEA was characterized by DSC, IR spectrophotometer, flow tester and the analysis of amino group. The results are summarized as follows. Melting point decreased with the increase of oligoamide of PEA polymers, while amino end-group increased. Glass transition temperature, melt-viscosity and ratio of aromatic ester to aliphatic ester content decreased with the increase of oligoamide of PEA polymers till 50%, but increased thereafter. Differences of ester content between oligomer mixtures and PEA polymers increased with oligoamide molar fraction till 50%, but increased thereafter. PEA of 50% oligoamide has the least value of(r). We can infer that ester-amide interchange occurs during polymerization of oligomers, from the fact of decrease of the ratio(r) of aromatic ester to aliphatic ester.