Distribution networks are commonly passive, so their disconnection from upstream network would make the loads and network components de-energized. By connection of the Distributed Generation (DG) to the distribution feeders, these networks are not passive anymore and if they lose their connection with the upstream network, loads are still supplied by distributed generation, thus islanding occurs in the system. Considering that usually in islanding, distribution systems do not have voltage and frequency control facilities, system’s operating in islanding is not acceptable and in order to prevent network, loads, and distributed generation damages, it would be necessary to disconnect these sources from the network as soon as possible. For this purpose, distributed generation will be equipped by the anti-islanding protection system. This system can be formed based on a communication infrastructure or designed according to the measured local parameters at the distributed generation terminal. Local methods are justify; LINE-HEIGHT: normal; TEXT-INDENT: 28.1pt; MARGIN: 0cm 0cm 6pt" This thesis introduces and investigates different aspects of the most widely used passive methods in islanding detection of synchronous distributed generation, such as; frequency, rate of change of frequency, vector surge, and voltage relays. In this regard, the theoretical basics and algorithms of each relay are analyzed. Furthermore, relays performance in islanding detection is investigated with using the performance curve and the Non-Detection Zone (NDZ). The behavior of these relays against occurrence of the non-islanding disturbances in system is studied also. In order to satisfy these purposes, two test networks is employed, one of them is common in related studies and the other one is a small part of Isfahan network. Transient interval simulations for the various islanding and non-islanding disturbances have been done in MATLAB/Simulink software. Finally, setting of various relays by means of the application region, is done for the test networks, considering the following goals: islanding detection in appropriate time, satisfaction of the requirements related to the safe and abnormal frequency and voltage variations, and ability in discrimination between islanding and non-islanding disturbances. Then, relays performance is investigated by usage of the power imbalance application region. Key Words Frequency relay, islanding detection, non-detection zone, passive methods, performance curve, synchronous distributed generation, voltage relay.