The strength of glass fiber used in composite leaf springs was measured after and before the manufacturing process. From the experimental data, the Weibull distribution parameters were estimated by graphical regression, non-linear regression and maximum likelihood methods. Correlations between the experimental data and distribution functions based on different regression techniques were compared.The fibers were found to have lost approximately 30% and 25% of their original strength after the fabricating and the molding process, respectively. Additional experiments showed that the impregnation system, the wipe-off system and the creel surface contact all adversely affect the fiber strength. Fractography and the introduction of flaws on glass fiber samples confirmed that surface defects were caused by the processing and resulted in the strength loss.