The paper deals with investigations concerning the structure and state of dispersive precipitations of the phases consolidating in the high-strength steel Weldox 1300 after its high temperature thermomechanical treatment.Making use of transmission technique of electron microscopy (TEM) mainly the microstructure and morphology of martensite was analysed,as well as the state of dispersive precipitations of carbides and nitrides resulting from microadditives of such alloys as Nb,V,Ti or B,introduced into the steel.Observations revealed both a fine lathed and twin structure of the matrix of martensite in the investigated steel.By means of the method of electron diffraction particles of secondary strengthening phases of the M(C,N) type of a nanocrystalline size could be identified,and also non-metallic oxide inclusions,affecting the mechanism of strengthening of the investigated steel. The paper deals with perturbations concerning the structure and state of dispersive precipitations of the phases consolidating in the high-strength steel Weldox 1300 after its high temperature thermomechanical treatment. Making use of transmission technique of electron microscopy (TEM) mainly the microstructure and morphology of martensite was analyzed as well as the state of dispersive precipitations of carbides and nitrides resulting from microadditives of such alloys as Nb, V, Ti or B, introduced into the steel .Observed revealed both a fine lathed and twin structure of the matrix of martensite in the investigated steel.By means of the method of electron diffraction particles of secondary strengthening phases of the M (C, N) type of a nanocrystalline size could be identified, and also non-metallic oxide inclusions, affecting the mechanism of strengthening of the investigated steel.