The thermolysis of β-pinene and the co-thermolysis of an equimolar mixture of β-and α-pinenes in supercritical ethanol were carried out. The reaction of β-pinene affords β-myrcene as the major product (>70%). Considerable differences in the temperature dependence of the reaction rate were revealed for the transformations of β-pinene into β-myrcene and of α-pinene into limonene. The pre-exponential factors and the activation energies were calculated. The enantiomeric ratios of the thermolysis products of β-and α-pinenes and limonene were estimated. The starting monoterpenes do not undergo racemization during thermolysis. The thermolysis of enantiomerically pure α-pinene affords racemic (±)-limonene, whereas (−)-β-pinene gives (−)-limonene. The enantiomeric ratio in the latter remains equal to the enantiomeric purity of the starting β-pinene.