The miscibility, the thermal degradation and biocompatibility of the blends of two biodegradable and bioreabsorbable polymers, brittle polyhydroxybutyric acid (PHB) and flexible poly (p-dioxanone) (PPD) are reported. The blends were prepared by casting from chloroform solutions and analyzed by differential scanning calorimetry, dynamic mechanical analysis, scanning electron microscopy and thermal gravimetric analysis. The blends are immiscible and present promising morphology of a dense phase and a microporous phase, one or the other being the matrix, depending on the composition. Despite the immiscibility, the thermal stability under an inert atmosphere is improved for both polymers. The results obtained from toxicity tests showed that PHB/PPD blends do not present indirect or direct cytotoxicity as a substrate for cellular growth.