Ultrathin fibers with diameters ranging from submicron to several nanometers, which are fabricated by an electrospinning technique, have received tremendous attention in biomedical fields in recent years. In the pharmaceutical and medical fields, for example, this technique can be used to make wound dressings, drug delivery materials and tissue-engineering scaffolds. Producing the yarn from nanofibres is considered as one of the great potentials in electrospinning. These yarns can be used in various fields of medical applications such as surgery sutures and drug delivery systems. Both natural and synthetic materials have been investigated for use as sutures in the past few years. Amongst them, biodegradable synthetic polymers offer a number of advantages over more conventional materials for developing sutures. In this research, we carried out electrospinning by using two differently charged nozzles to produce PLGA (10/90) nanofibers yarn. PLGA nanofiber yarn has the potential to be applied in medical fields especially as absorbable suture. Various electrospinning parameters such as solution, applied voltage, feed rate, distance of two nozzles and distance between nozzle and collected drum were optimized to produce good quality yarn. Then, mechanical properties of yarn such as straight and knot strength, breaking elongation, work of rupture and elastic modulus were studied. In order to improve the properties of this yarn, heat setting process was done. To achieve these goals, we developed the heat setting setup. Two heat-setting techniques, using heat water and dry heat, were tried and the influence of the heat setting process on the mechanical properties of yarn has been studied. Result has shown that heat setting with boiling water is better than other type of setting. The presence of a knot lowered breaking load and rupture occurred consistently at the knot region. Knot strength of two type of surgery knot (square and surgeon) showed square knot strength is greater than other type of knot. In vitro study of degradation behavior of nanofiber yarn showed fast decrease in its mechanical properties that can be due to great surface area of nanofibers exposed to surrounding environment. In the next section of research, nanoindentation test conducted on nanofiber yarn and braid vicryl suture (commercial suture) to compare behavior yarn associated with applied normal force. The result indicated elastic recovery of nanofiber yarn is less than braid suture. No capillarity is desired in any case of suture application due to the spread of microorganisms with the body fluid in between the fibers in multifilament sutures. In next approach, capillary rise in the nanofiber yarn and braid vicryl suture were studied. The results demonstrated nanofiber yarn has less capillarity than braid suture. Finally, Fracture morphology of nanofiber yarn has investigated. SEM images were used to analyze the broken ends of the yarns. Observations showed fracture morphology of yarn is very similar to stake-and-socket mechanism. With analyze of fracture morphology of single nanofiber, mushroom ends were seen as normally associated with high-speed breaking of ductile filaments