Insertion of DGs in distribution system provides many potential benefits such as peak shaving, improvement of power quality and reliability, increased in efficiency and improved environmental performance. However, it is followed by some special problems. Perhaps, the most important problem in using DGs in distribution systems that may disturb system protection is islanding. Islanding operations of DG usually occur when power supply from the main utility is interrupted due to several reasons but the DG keeps supplying power into the distribution networks. An islanding situation should be detected as soon as the island is formed. In this paper, a new hybrid islanding detection method for synchronously rotating DGs is proposed. The proposed method effectively combines the principles of active and passive methods. This method is tested under various operation conditions. Simulation results show that the method correctly detects the islanding operation and does not mal-operate in the other disturbances such as short circuit, load variations, capacitor switching .