The potato starch has been subjected to plastification with glycerol using twin-screw extruder in different conditions. The structure of obtained samples has been determined by Fourier transform infrared spectroscopy with attenuated total reflectance methods. The average molecular weights by chromatographic method and solubility in water have also been determined. Next, the susceptibility of all samples to activity of microorganisms such as bacteria, fungi, and actinomycetes has been checked. It has been stated that increasing rotation speed of extruder screws causes the degradation of starch slightly, influencing the later bio-decomposition. The actinomycetes are the most effective in this process. POLYM. ENG. SCI., 52:2537-2542, 2012. (C) 2012 Society of Plastics Engineers