The influence of a strong/weak interface ratio on the mechanical properties of Si3N4/BN-based layered composites was studied. The ratio was controlled by the number of BN spots between the adjacent Si3N4 layers. By increasing the BN interface area from 0% to 72%, fracture toughness increased from 7.7 to 10.9 MPa.m(1/2), and bending strength decreased from 1275 to 982 MPa. Fracture toughness was improved from 8.6 to 10.1 MPa.m(1/2) by additional heat treatment of samples containing 2 vol% beta-Si3N4 seed particles. The bending strength of samples with 35% weak BN interfaces, measured perpendicular and parallel to layer alignment, was 1260 and 1240 MPa, respectively. This confirmed the two-directional isotropy of layered samples.