Atactic poly(methylmethacrylate), aPMMA, was blended with poly(3-D(Ϫ)hydroxybutyrate), PHB, up to a maximum composition of 25% of polyester, at 190°C in a Brabender-like apparatus. The resulting blends quenched from the melt to room temperature were completely amorphous, and exhibited a single glass transition using DSC and DMTA, indicating miscibility of the components for this time-temperature history. Tensile experiments showed that at room temperature the 10/90 and 20/80 PHB/ aPMMA blends exhibited higher values of strain at break, and slight decreases of the modulus and stress at break compared to neat aPMMA. The tensile energy at break was almost twice that of neat aPMMA. Tensile tests were also performed at 80°C, at which point the 25/75 and 20/80 PHB/aPMMA blends are above T g , while the 10/90 and neat aPMMA are below T g . The stress-strain curves obtained were functions of the physical state of the amorphous phase, and also depended on the difference between the test temperatures and T g . In particular, comparing the neat aPMMA and the blends, decreases of the modulus and stress at break and a respectable increase in the strain at break were observed in the latter. Finally, the results were commented considering the thermal degradation of PHB in the melt during the blend preparation.