Blends of cellulose acetate (CA) and poly(3-hydroxybutyrate) (PHB) were prepared by the solvent-casting method in both the presence and the absence of a compatibilizer agent. The compatibilizer was synthesized by reactive processing between CA and PHB. From the differential scanning calorimetric analysis, it has been identified that CA/PHB blends are immiscible in the range of PHB content studied. The existence of interactions between the components was observed due to the displacement of glass transition temperature relative to PHB phase in the blend. The grafting copolymer promoted the increase of interactions between the phases specifically to compatibilized CA/40% wtPHB blend. This composition shows significant changes in crystalline percentage compared to the uncompatibilized blend. The existence of phase interactions modified the viscoelastic behavior of the compatibilized blends by introducing changes in the chain segment mobility due to the addition of compatibilizer as the dynamic mechanical analysis has pointed out. It was observed that different of the blends with lower PHB content, CA/40% wtPHB compatibilized blend with same compatibilizer content did not reach PHB saturation. This difference in behavior can be attributed to the fact that the content of compatibilizer agent used was the proper amount to promote both PHB domain size reduction and dispersion. (C) 2016 Society of Plastics Engineers