Poly (3-hydroxyburate) (PHB) and its copolymer with 3-hydroxyvale-rate (P(HB-HV)) have attracted much attention because they are thermoplastic bio-polyesters．It has been reported that Poly (3-hydroxyburate) (PHB) and Poly (eth-ylene oxide) (PEO)，Poly (vinyl acetate) (PVAc) or Poly (vinylidene fluoride) (PVDF) are miscible in the melt，they all exhibit a single glass transition temperature．In this paper，we report the results of an investigation concerning the phase structure and miscibility of blends obtained by mixing PHB with uncrystallized com-ponent Poly (hydroxy ether of bisphenol A) (PBHE)．It is found that PHB and PBHE are partially miscible by the results obtained from DSC and FTIR measure-ments．In comparison with the samples cast from solution，the annealled samples display higher degree of crystallinity and better miscibility (Fig．1)．The results of FTIR measurements indicate that there are no hydrogen bonds between the carbonyl groups of PHB and hydroxy groups of PBHE in the cast sam-ples．But some interaction between the segments of two polymers are formed，because the wave numbers of some groups of PHB and PBHE change regularly with the inc-rease in the content of PHB in the blends (Tab．1)．The crystallite sizes of the annealled samples are listed in Table 2．Increasing the uncrystallized component in the blend from PHB／PBHE=100／0 to PHB／PBHE=50／50．it is observed that the crystallite sizes of (020) and (130) crystal faces be-come larger，and larger，which reach the largest sizes at the composition of PHB／PBHE=50／50．On the contrary，increasing the uncrystallized component from PHB／PBHE一40／60 to PHB／PBHE=20／80，the crystallite sizes get smaller．Data from SAXS experiments indicate that the thickness of the interphase of pure PHB is 1.5nm and that of the blends are about 2.0nm；the period of C axis of a PHB orthorhombic cell is 5.96A，therefore the interphase consists of three lat-tice layers．This agrees with the results predicted theoretically by Paul J．Flory and Do Y．Yoon．The lamellae of PHB／PBHE=50／50 is the largest in thickness in all blends．With the increase in uncrystallized component，the lamellae of the blends change similarly as the crystallite sizes discussed above．In all blends，the density dif-ference of PHB／PBHE=75／25 composition between crystalline and amorphous pha-ses is the biggest．This agrees with that the degree of crystallinity for PHB／PBHE=75／25 composition，obtained by DSC measurements，(Tab．3)．