The thermal properties change after the soil burial degradation of polylactic acid plasticized with tributyl o-acetyl citrate (ATBC) was studied By differential scanning calorimetry (DSC). The results have been corelated with those obtained by weight loss measurements, changes in average molecular weight and its distribution, mechanical and surface properties correlated with structural and morphological modifications. The Young modulus increases during degradation time while elongation at break significantly decreased, mainly for the biocomposites with high content of chitosan which also led to important decrease of average molecular weight and increased polydispersity index. The high content of chitosan led to increased hydrophilicity of biocomposite surfaces which favors interaction with moisture and attack of microorganisms. Besides the loss of transparency at the end of biodegradation test that all composites became brittle. This is also demonstrated by increase of glass transition temperature and crystallinity degree values and decrease of cold crystallization and melting temperature when soil burial period is longer. Degradation in active soil is much advanced than in sterile soil this being due to the microorganisms action. Chitosan as hydrophilic compound promotes the soil burial degradation of PLA. However longer period of soil burial are necessary for totally degradation of the plasticized PLA/CS biocomposites.