Poly(3-hydroxybutyrate) PHB and poly(p-dioxanone) PPD are examples of promising polymers in tissue engineering. The purpose of this work is to synthesize polyurethanes which combine stereoregular and rigid blocks of PHB with stereoregular and flexible blocks of PPD. In order to guarantee stereoregularity, polyols from PHB and PPD were obtained from mass reduction via sodium borohydrate. This route allows us to obtain bifuncional polyols. The polymer molar mass reduction using this strategy was effective, however secondary and non reactive products with diisocyanate like insaturated acid were formed as shown by mass spectroscopy data. The products of mass reduction were characterized by H1 NMR, FT-IR, DSC and MALDI-TOF/MS. The PU's were synthesized reacting the polyols with hexamethylene diisocyanate (HDI) and they were characterized by FT-IR, H1 NMR, DSC and XRD.The PU obtained from PHB and PPD polyols presents two crystalline phases, corresponding to both polyester blocks. The introduction of flexible segments of PPD in polyurethane, affected the characteristics of crystalline phase formation of PHB, increasing the melting point of this block in comparison with the pure PHB polyol, probably by increasing the crystallization rate.