A silicon nitride-silicon carbide nanocomposite has been prepared by an in situ method that utilizes C+SiO2 carbo-thermal reduction during the sintering process. The materials consist of a silicon nitride matrix, with an average grain size of 140 nm, and inter- and intragranular SiC particles with sizes of approximately 250 and 45 nm, respectively. The four-point bending strength and its distribution were investigated. The fracture origins were identified and characterized using fractographic methods, and a fractographic montage of the Weibull plot and fracture origins was constructed. The fracture origins were subsurface and volume located processing defects with sizes from 5 to 460 mu m, mainly in the form of clusters of pores, together with clusters of large SiC grains.