The change in microhardness of initial n- and p-type silicon containing phosphorus and boron impurities during neutron transmutation was investigated. It was found that doping silicon with the stable isotope ³¹P, regardless of the phosphorus content in the original crystal, leads to an increase in the microhardness of n-Si<P>. For p-type silicon containing boron impurities, microhardness is determined by the ratio of boron and ³¹P isotope concentrations. It was established that in p-Si<B>, an increase in microhardness of neutron-transmutation p-type silicon is observed when the concentration ratio N_³¹P/N_B>1. The mechanism of transformation of radiation-induced and intrinsic defects responsible for the change in microhardness of n- and p-type silicon during neutron transmutation is discussed. Keywords: monocrystalline silicon, impurity, neutron-transmutation silicon, doping, isotope ³¹P, concentration, microhardness.