Testing methods for crack-growth resistance-curve (R-curve) behavior were investigated and developed to analyze the toughened mechanism in polycry stalline ceramics. These methods are a biaxial-flexure method for small-scale disc-shaped specimens with micro-indentation cracks and a single-edged notched beam flexural method with crack stabilizers. In both methods, the growing crack length is measured directly as a function of applied stress, using the system that consist of a microscope and a CCD camera. Applying these testing methods, R-curve behavior of a toughened silicon nitride with a preferred orientation of elongated grains was evaluated to characterize the toughened mechanism, comparing with the behavior in a commercially available silicon nitride. The behavior having these rising R-curves is discussed with emphasis on the effects of microstructure such as grain-growth and grain-orientation, and resultant grain-bridgings behind the crack-tip.