A plasticizer, polyethylene glycol ( PEG), was used to disperse multiwalled carbon nanotubes (MWCNTs) in biodegradable poly(L-lactide) during one-step melt mixing. Incorporation of PEG significantly promotes the formation of a percolating MWCNT network in the plasticized composites, as revealed by rheological measurements and morphological observations. It, in turn, results in the retarded glass transition and cold crystallization behaviors in these plasticized composites as a result of constrained chain relaxation. It is believed that noncovalent wrapping of MWCNTs by PEG is responsible for the improved affinity between MWCNTs and the poly(L-lactide) matrix. (C) 2011 Wiley Periodicals, Inc. J Appl Polym Sci 123: 1843-1847, 2012