We consider a plate with a side crack directed at 45° with respect to the principal directions of orthotropy. A tension force that is orthogonal to the direction of the crack loads the plate. We obtain the stress intensity factor and the mode of crack propagation. From the calculations it follows that the degree of orthotropy of the plate material affects slightly on the stress intensity factor. When the load reaches some magnitude, the crack propagates along a principal direction of orthotropy corresponding to the less strength (in the case under consideration, in the direction of principal reinforcement). At that, at the initial stage of crack propagation, the matrix not the fibers fail.