There has been an upsurge in the application of composite materials in the last few decades, due to high demands on material performance placed by advanced technologies. Most of these applications include the situations where degradation of strength and life by fatigue process is most likely. This work presents results of rotating bending fatigue tests conducted on two types of unidirectional glass fiber reinforced polymeric composites, having Vinylester and Epoxy as matrix materials. It has been observed that the probabilistic distribution of fatigue life of these glass fiber reinforced composites, at a particular stress level, can be modeled by two-parameter Weibull distribution, with statistical co-relation coefficient values exceeding 0.90. Various methods have been used to obtain the parameters of Weibull distribution. Kolmogorov-Smirnov Goodness-of-fit test has also been used to reinforce the above findings. The two-parameter Weibull distribution has also been employed to incorporate failure probability into S-N relationships.