Poly(3-hydroxy octanoate) (PHO), poly(3-hydroxy butyrate-co-3-hydroxyvalerate) (PHBV), and linoleic acid were grafted onto chitosan via condensation reactions between carboxylic acids and amine groups. Unreacted PHAs and linoleic acid were eliminated via chloroform extraction and for elimination of unreacted chitosan were used 2 wt % of HOAc solution. The pure chitosan graft copolymers were isolated and then characterized by FTIR, C-13-NMR (in solid state), DSC, and TGA. Microbial polyester percentage grafted onto chitosan backbone was varying from 7 to 52 wt % as a function of molecular weight of PHAs, namely as a function of steric effect. Solubility tests were also performed. Graft copolymers were soluble, partially soluble or insoluble in 2 wt % of HOAc depending on the amount of free primary amine groups on chitosan backbone or degree of grafting percent. Thermal analysis of PHO-g-Chitosan graft copolymers indicated that the plastizer effect of PHO by means that they showed melting transitions TmS at 80, 100, and 113 degrees C or a broad TmS between 60.5-124.5 degrees C and 75-125 degrees C while pure chitosan showed a sharp T-m at 123 degrees C. In comparison of the solubility and thermal properties of graft copolymers, linoleic acid derivatives of chitosan were used. Thus, the grafting of poly(3-hydroxyalkanoate) and linoleic acid onto chitosan decrease the thermal stability of chitosan backbone. (C) 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 81-89, 2007