1. Equipment was developed and the test procedure proposed for fracture toughness testing compact specimens of structural materials in off-center loading at low temperatures down to 4.2°K. 2. The strain gauges and dynamometer operating-directly in the cryogenic liquids were produced and calibrated at various temperatures. These devices can be used to record the (P−V) and (P−f) diagrams during testing. 3. Preliminary tests were carried out on the specimens of 03Kh18N16G4A and 03Kh18N6G4 steels at 300, 77, and 4.2°K. The cracking resistance of the tested specimens at 4.2°K was evaluated on the basis of the values of KIc whereas the parameters KQ and KC* were used for evaluation at 77 and 300°K. 4. The results show that 03Kh18N16G4A steel at 4.2°K has the optimum high values of both the yield stress (1600 MPa) and fracture toughness (104 MPa·m1/2). Having relatively high values of σ0, 2 (1400 MPa), 03Kh18N6G4 steel has at 4.2°K unacceptably low freacture toughness parameters indicating that the steel fails by brittle fracture in these conditions.