The rheological properties of two commercially available biodegradable polyesters-poly(lactic acid) (PLA) and aliphatic-aromatic co-polyester Ecoflex (TM)-have been investigated. The rheological study was focused on measuring the viscosity and examining sharkskin, melt fracture, and extrudate swell phenomena, which are crucial in industrial applications. The experiments show that the two biodegradable polyesters exhibit shear-thinning behavior similar to other polymers and the Cox-Merz rule is obeyed. It was observed that with increasing shear rate PLA exhibits sharkskin and gross melt fracture while Ecoflex (TM) exhibits only gross melt fracture. Experimental results indicate that both biodegradable polyesters exhibit small extru-date swell, up to 28% for PLA and up to 34 % for Ecoflex (TM).