Rate constants of thermal isomerization of 6-phenyl-1,5-diazabicyclo[3.1.0]hexane into 1-(benzyl)-4,5-dihydro-1H-pyrazole at convection and microwave heating in toluene and chlorobenzene (solvents) were determined within the temperature range 90°C to 120°S. These data were used for the calculation of activation parameters of isomerization. It is shown that microwave heating increases the rate constants at the same temperature by a factor of 2 to 2.5 as compared with those using convection heating. The reason is that the effective temperature of microwave heating exceeds that of convection heating by 6°C to 9°S in toluene and by 12°C to 20°S in chlorobenzene as solvent.