From a microscopic point of view, composite materials generally contain innumerable defects in itself, but even if they have some defects, many of them are sometimes almost harmless depending upon types, locations and applied conditions. On the other hand, in a stress concentrated region, even a very minute defect often causes a crack growth and then arrives at a fatal size. So it is impossible to estimate the strength reliability of composite materials until the extent that every type of defect takes part in a catastrophic fracture is predicted and examined. For this purpose, the present paper aims at estimating the strength reliability of composite materials containing defects in itself on the basis of a stochastic tensile failure process simulation of unidirectional fiber reinforced composites which was described in the previous report. Each type of defect modes of composite materials has been classified and modelized systematically, and the damage tolerance has been examined as follows : a goodness of fit has been investigated for statistical distributions on each type of defect mode, which gives the difference in goodness of fit due to the number of included defects or the sample size. As for a decrease in the strength reliability due to defects, the effect of fiber and matrix defects has been examined in detail. And finally, a comparison has been tried among each type of defect modes by means of the PDF curve, which has been shown to be useful to a certain extent in discriminating a defect mode.