Different researches show that at least half of the couples referring for infertility investigation and treatment have a causative male factor. Male factor infertility can be caused by a variety of defects, e.g. abnormal sperm amount, morphology abnormality or low functionality. In all cases where the sperm cannot reach the ovum, in vitro fertilization (IVF) technique can be used for fertility. Separation of motile sperms from non-motile ones is essential in some infertility treatments such as intracytoplasmic sperm injection ( ICSI) and in vitro fertilization. where as motility is one of the most important parameters in sperm quality, so the effective and safe operatio are more desirable in such treatments. The ideal sperm separation technique should be easy, low-cost, separate much sperms as possible, not damage the sperms, not cause physiological transformation, eliminate dead sperms and also other cells, allow analyzing larger volumes of ejaculates, reduce the risk of reactive oxygen species and not having toxins for spermatozoa. In addition after the separation step spermatozoa must be viable and be able to fertilize the egg. Sperm morphology is directly related to the successful process. A system that selects the best sperms for fertilization can help to increase the rate of birth. In addition, sperm separation is a basic step in the IVF process. Several methods for motile sperm separation have been reported, including : Sperm washing, Sperm migration, Sperm sedimentation, Filtration, Density gradient centrifugation, Sperm surface charge for sperm selection(electrophoresis zeta), Magnetic-activated cell sorting (MACS), Hyaluronic acid sperm binding, Raman spectroscopy, Confocal light absorption and scattering microscopy (CLASS) and Selection based on live sperm morphology. Sperm migration and movement from one point to another, is one of the sperm separation methods. Migration method, as a method to separate motile sperms, is used as an ideal experimental sperm selection method. One of the emerging systems used for motile sperm separation is sperm separation microfluidic system. among methods of motile sperm selection the ones which use micro channels go beyond others in simplicity, user friendliness, and similarity to the physiological environment. Seo et al, designed a motile sperm sorting microfluidic system (MSMS) consisting four channels and three reservoirs. The flow in channels is created by hydrostatic pressure of columns at the liquid reservoirs.In this system a reverse stream is flowing and only motile sperms are able to swim against the flow. In this thesis, we will simulate and develop the MSMS micro fluidic device that, previously reported by Seo. After validation with Seo’s results, we optimize the size of micro channels. The results will be useful in sperm sorting applications The following study reviews strengths and weaknesses of this method and offers a new method for motile sperm separation based on the method proposed by Xie et al. The device is modeled by Gambit software and then is analyzed by the Fluent software. The results suggest the optimal length for the main and side channels, and are in good agreement with the literature. In addition following thesis proposed a new system to sperm selection, that is based on sperm motility and electrophoresis phenomena. This proposed system is more comprehensive than other sperm selection systems. keywords: IVF, Motile Sperm, Sperm Selection, Microfluidic, Chemotaxis,Separation, Electrophoresis