The postulation of Dark energy and Dark matter on the basis of observational results does not end the mystery of their existence. Theoretically new insights into dark matter have been achieved analyzing recent experimental data from the cosmic ray physics. It has been shown that, if the dark matter is a hidden scalar field, then it is not only possible to explain the ATIC/PPB BETS excess but also the observed dark matter abundance naturally and simultaneously. Being motivated, mainly by the assumption of hidden scalar field and some associated works, we consider the Modified Chaplygin Gas for some thermodynamical analysis. The point that if the scalar field is assumed to oscillate before the reheating was not completed, i.e., T_R <= 10^10 GeV, the abundance of dark matter would be diluted by the entropy production during reheating indicates the importance of thermodynamical analysis. We, assuming the properties of Modified Chaplygin Gas, derive an expression for the second law of thermodynamics. It is observed that it also sheds some new lights on Generalised Second Law.