Due to outstanding advantages of polymeric insulators such as: hydrophobicity, impact resistance and lower weight, their application in the high voltage transmission and distribution lines is increased significantly, in recent years. The most important feature of these insulators is their hydrophobicity. Contamination and aging are some of the factors that weaken this important feature and reduce the reliability of these insulators. Due to aging effects partial discharges start on the surface of the composite insulators and increase by impact of external factors. This paper examines the occurrence of partial discharge signals on polymeric insulators under: varying amounts of contamination, impact of physical defects, and accelerated salt-fog aging process. The partial discharge signals of these insulators are detected by UHF antenna and they are recorded. These measured partial discharge signals are used to monitor the insulation status. Their characteristics are determined through feature extraction. Using these "extracted features", a good distinction is found among these captured signals; which relate to different samples characteristics in terms of: severity of pollution, or different mechanical defects. These features are selected and used for classifying the insulators condition by support vector machine (SVM) algorithm.