The fracture behaviour of brazed joints of the soft martensitic stainless steel X3CrNiMo13-4 under cyclic loading is investigated. The fatigue crack propagation curves (da/dN-ΔK) were derived for different load ratios R. The fatigue crack threshold values ΔKth were estimated to be 9 MPa m0.5, 7 MPa m0.5, 6 MPa m0.5 and 4 MPa m0.5 for the R values of 0.1, 0.3, 0.5 and 0.7, respectively. In addition, crack growth curves were derived for different constant loads ΔF. The Paris exponent, n, was estimated for the different R values and found to be very high compared to homogeneous materials. The work was completed with microstructural and fractographic investigation by scanning electron microscope (SEM).