Development of precise calorimetry has enabled us to understand the stability of three-dimensional structure, catalytic activity, and molecular recognition of biomolecules. We have developed isothermal acid-titration calorimetry (IATC) to evaluate the pH dependence of protein enthalpy and demonstrated the thermodynamic transition between the native and the molten globule (MG) state of cytochrome c with very small enthalpy change (～30 kJ/mol) by this method. The double deconvolution method with precise differential scanning calorimetry (DSC) has revealed the MG state as an equilibrium intermediate state of the reversible thermal transition of the protein and pressure perturbation calorimetry (PPC) has succeeded to determine its volumetric properties. The hydrolytic activity of cellulase against a kind of oligo-cellulose can be quantitatively evaluated using dynamic feature of isothermal titration calorimetry (ITC) and a kinetic equation for enzymatic reaction. We developed a new multi-binding model and succeeded to characterize the interaction between adenosine 5’-triphosphate and magnesium ion. These examples strongly indicate the importance of precise calorimetry in the field of protein research.