Department of Chemistry, University of Kalyani, Kalyani-741 235, West Bengal Manuscript received 21April 1980, revised 16 April 1981, accepted 15 July 1981 Rates or decarboxylation or malonic and substituted malonic acids, methylmalonic acid, dimethylmalonic add, ethylmalonic acid and benzylmalonic acids in molten state have been followed at several temperatures by measuring the volume or co. evolved at various times. Employing Eyring equation, the thermodynamic parameters have been evaluated Decarboxylation kinetics or malonic acid in liquid crystal solvent Is also reported.