In the previous papers, the brittle fracture initiation characteristics of plates with an inclined crack under bi-axial tension were studied. This condition led to the brittle fracture under the combination of opening (Mode I) and sliding (Mode II) modes. In this paper, brittle fracture under all possible combination of opening, sliding and tearing (Mode III) modes is investigated both theoretically and experimentally. Using specimens of PMMA, fracture tests under pure Mode II, pure Mode III, the combination of Modes I and II, and that of I, II and III are carried out. Then, the test results are compared with those predicted by the fracture criteria based on : (1) maximum tangential stress, [σ_θ] _max, (2) maximum energy release rate at the propagation from a small kinked crack, [ G ^B (γ)] _max, and (3) maximum energy release rate at the initiation of small kinked crack, [ G (γ)] _max. The following conclusions are drawn from the results of the investigation. (1) The measured fracture stresses under an arbitrary combination of the crack face displacement modes are in good agreement with those predicted by [ G ^B (γ)] _max or [ G (γ)] _max concepts. These energy release rates are expressed in the closed forms, and can be applied to any crack under arbitrary combination of modes. (2) Although [σ_θ] _max concept is extended for the combined modes including Mode III, this is not effective except for the combination of Modes I and II. (3) The interaction curves of fracture strength under arbitrary combination of Modes I, II and III are obtained based on [ G ^B (γ)] _max and [ G (γ)] _max concepts.