Miscibility, molecular interactions and crystallinity of blends of poly(3-hydroxybutyrate) [P(3HB)] with poly(3-hydroxybutyrate- co-3-hydroxyvalerate) [P(3HB- co-3HV)] were studied in this work. P(3HB)/P(3HB- co-3HV)-6%3HV blends were prepared by casting and characterized by differential scanning calorimetry (DSC) and X-ray diffraction (XRD). The results for the glass transition temperatures ( T g) and the melting temperatures ( T m) showed that most of the blends are miscible in amorphous and melting phases. A good agreement between values of experimental T gs for miscible blends and those predicted by Fox equation was achieved. XRD analyses confirmed the crystallinity degrees found by DSC. Measurement of T m depression for the blends allowed to determine the Flory-Huggins interaction parameter ( χ 12) using the Nishi-Wang equation. The value of χ 12 obtained is negative, indicating miscibility of the components of the blends, which is in agreement with DSC experiments.