The crystalline structures of the hot-melting adhesive fibers of two series of copolyesters have been studied by wide angle X-ray diffractive technique. Their melting behavior has been investigated by Differential Scanning Calorimetry(DSC). The mechanism of the lowest melting behavior in the series was revealed. The experiments indicated that in most cases

the crystallization in fibers was carried out from one type of the structural repeat units in fibers.The fibrous samples in each series can be divided into two parts according to the lowest melting temperature. The melting point fusion heat and crystallinity of the fibrous samples in each part changed regularly with varying mol% of 1

6-haxane diol to 1

4-butane diol in the ini-tial monomer feed. The mechanical properties of fibers were related to their crystallinity. While the not-melt adhesive performance was dependent on the non-crystalline region in the fibers.The adhesive effect was improved greatly with increasing the content of flexible component in non-crystalline region in the fibers.