Sembilan Island was one of the 17 islands located in the East Coast of North Sumatra. This island is surrounded by mangrove with varying thickness and density. Information on the identification and potential of mangrove in this island already reported but limited to a narrow area. Information about the value and status of mangrove ecology in this island have not been written, so it was needed to carry out for a study of mangrove ecological analysis. This information could be used later as a reference in sustainable mangrove management. The objective of the study was to determine the value and ecological status of mangroves. The research was conducted in September 2015. The data were collected at 9 sampling points namely; 4 points in the east, 2 points in the south and 3 points in the west part of the study areas. The spot check method was used in the study. The results showed that there were 28 species of mangrove belonging to 13 families. It's divided into 26 species of true mangrove and two species of associated mangroves. Mangrove’s zonation was Avicennia/Sonneratia on the front and ferns (A. Aureum and A. speciosum) in the section near the mainland. Mangrove thickness reached 134-1683 m. The density of mangrove was 333-4601 individuals/ha with the cover area of 2522-5810 cm 2/ha. The results of the importance index value of mangrove showed that A. marina has a great influence and role in the community of mangrove vegetation, especially in the eastern part. Therefore, the mangrove in Sembilan Island was categorized into damage to good condition. The good category was recorded in the western part of the island, while the damaged category was found in the east part of the island.