The thermodynamic analysis of the uniaxial stretching of block copolymers of various chemical compositions and hard block contents was carried out using a deformation calorimetry method. It was found that the initial small deformations result from the volume elasticity of the hard phase, independent of its content and chemical nature. The intramolecular energy contributions of soft blocks to the deformation thermodynamics were estimated. It was shown that the hard block contributions depend on their content and degree of sample stretching. The samples were divided into two groups with respect to their thermodynamic behavior.