Though the tensile strength of nanofibers is essential to determine their application fields, few studies have been conducted on this topic, due to the difficulties involved in the preparation of single nanofiber tensile specimens, the manipulation of the clamping device, and the sensing of the nano- force and strain. A bundle testing method was employed in this work to measure the tensile strength of nanofibers. For this purpose, a conductive substrate was designed to hold several thousand nanofibers extruded from a spinning nozzle and align them uniaxially during the electrospinning process. This substrate was designed for a dynamic mechanical analyzer (DMA), because most DMAs are equipped with fine sensors sensitive enough to measure a very small force and strain. Nylon 6 nanofibers were electrospun and collected on the substrate. Then, they were elongated simultaneously in the DMA until they were fractured, showing that the aligned nanofibers have superior tensile strength and modulus compared to their counterpart microfibers and thus suggesting that polymeric nanofibers have the potential to be used as reinforcement fibers for composite materials.