In this paper, the distribution suspension porecelain insulators which had been used for long periods in the contaminated area were evaluated. The contaminated area is close to the sea and in the high density of industries. The heavily contaminated domestic and imported insulators were investigated by using electrical characteristics, such as power-frequency dry flashover voltage, power-frequency wet, flahover voltage, and leakage current. Also, these electrical results were compared with the contaminants on the surface. From these analysis, we found that the contamination from the industrial dust, only slightly decreased flashover voltage and increased leakage current. Therefore, the electrical properties of insulators used for 30 years in the area of coast and industrial complex were not much changed.