This study evaluated how applying tension in the axial dimension during Natural Fiber Welding (NFW) of lignocellulose yarn impacted the fibers mechanical and morphological properties. Understanding the combined effects of applied tension and polymer mobilization is vital both for controlling sample contraction during NFW experiments, and will inform the design of scale-up processes that rely upon tension for pulling yarn and cloth stocks through continuous treatment. The tensile strength and Young’s modulus of the fiber-welded taut linen yarns slightly increased over the tension values for the untreated linen. The greatest increase in the tensile strength and Young’s modulus of the treated linen yarn occurred when taut linen yarn was treated with either 1-ethyl-3-methylimidazolium acetate or acetonitrile at 40 °C for 60 s. No tensile value improvements were observed in the NFW treated taut bamboo yarns. However, slight increases in the energy at break and tensile strength were observed when bamboo yarn was treated with methanol or warm acetonitrile. It is thought that the observed tension property differences between the treated linen and bamboo yarns is related to the cellulose and lignin content in the tested material.