owadays, urban electrical railway systems have rapid growth due to such advantages as traffic and pollution reduction. Electrical railway is considered the predominant part of traortation systems in large cities. Electrical railway is a complex system and constituted of several subsystems. Grounding system is one of the main parts of electrical railway systems that is the subject of this study. There are several important reasons why a grounding system should be installed. But the most important reason is to protect passengers against electric shock. Grounding system of electrical railway systems consists of two important parts, first is the AC grounding system that is used in passenger stations. The second are the rails as paths for traction current. This arrangement mainly fucuses on economic considerations, since it does not require the installation of an additional return conductor. The rails along the railway, which lie exposed on the ground, will cause rail potential and leakage of stray current to the ground. So the choice of grounding strategies within the electrical railway systems has a profound influence on rail potential and stray current control. This potential difference could cause electric shock for the passengers. The most important effect of stray current is corrosion of nearby buried metallic structures, such as pipelines and concrete reinforcement armatures. So the goal of this research is to study the methods to reduce the undesired effect of stray current to the ground. For this purpose, first electrical parameters of railway systems will be studied and short circuit current in AC and DC systems will be calculated. To analyze the operation of AC grounding system during a fault to ground, first the principles of design and analysis for grounding system will be reviewed and the impacts of different parameters on operation of this system will be analyzed. Finally AC grounding system of Esfahan urban railway will be studied for controlling of dangerous voltages. Then, some techniques will be proposed to improve the operation of the grounding system. For reducing the rail potential and stray current in DC electrical railway systems, the methods of modeling the rail-ground system and the impacts of different parameters will be studied. Then Esfahan urban railway as a practical case is simulated and rail potential and stray current in this system will be evaluated. In practical systems, methods such as voltage limiting devices and stray current collection mats are used to control rail potential and stray current. Voltage limiting devices are located between rails and ground so that when the rail voltage exceeds the allowable limit, establish a direct connection between rails and ground to eliminate the risk of electric shock. Operation of the voltage limiting devices cause increasing stray currents. Stray current collection mats could be constructed under the rails in order to absorb the stray currents and avoid damage to metallic structures. Adequacy of these practical methods will be studied. At the end, new methods are proposed to improve the operation of voltage limiting devices and stray current collection mats in urban electrical railway systems. Keywords: Electrical railway systems, Grounding system , Stray currents, Rail potential, Safety