The continued search for sustainable and eco-friendly materials led to the integration of bio-fibers as the reinforcement in composite materials. However, a wide variation in their mechanical properties poses a considerable challenge for their incorporation in load bearing and structural bio-composite materials. In this thesis, a rigorous experimental investigation is performed for quantifying this variation in mechanical properties of flax fiber such as ultimate strength, ultimate strain, and elastic modulus. The effect of stalk diameter and variety on strength and strain was investigated on a statistical basis. Probability distribution models were proposed for predicting the probability of failure on a given strength. A dynamic in-situ failure analysis was performed on technical flax fibers with the help of scanning electron microscopy (SEM) to investigate the micro and nanoscale failure behavior. A reliable measurement method of surface energy of a single flax fiber was proposed and performed by atomic force microscopy (AFM).