The behaviour of a propagating crack when an interface is present is a key feature in composite materials. This interaction usually predetermines final fracture behaviour of the material. In case of ceramic based composites (particle, fibre reinforced, laminates etc.) knowledge about properties of the interface and/or interlayer is usually unknown due to difficulties associated with their experimental determination. The aim of this work is to indicate a possible way for the determination of interface characteristics suitable as inputs for numerical calculations. The introduced testing methodology was tested on spinel composite ceramics reinforced by unidirectional SiC fibre. The adopted method for fracture toughness determination is using a chevron notch technique. Additionally, fractographical techniques were used when interpreting the measured values.