Abstract. Wahyuningsih H, Sinaga SMS, Hartanto A. 2022. Ichthyofauna diversity in Pematang Matik Coastal Waters, Serdang Bedagai District, North Sumatra. Biodiversitas 23: 4992-5000. Pematang Matik Coastal waters are coastal areas that have a major role in the life of various fish species. Research on fish diversity in coastal waters is very important in order to gain a better understanding on the fish diversity in coastal areas such as North Sumatra, including Indonesia. The objective of this study was to initiate an inventory of fish species, their abundance and assessment of its biodiversity based on Shannon's diversity index (H'), and evenness index (E) in Pematang Matik coastal waters. The research was conducted from September to October 2021 at four stations with different human activities by the coastal community. Fish samples were taken using fishing nets that were installed for 12 hr with two replications. In this study, 21 species of fish from 19 families were identified. The highest abundance of fish was obtained from the Mugilidae family, namely Crenimugil crenilabis and Liza macrolepis. The fish diversity index obtained was 2.19-2.95, while the uniformity index obtained was 0.719-0.968. The values ??of H' and E at Station 4 (absent from any human interferences) have higher values ??than the other three stations. The diversity, as expressed in H' value in four research stations, indicates that the coastline has a high diversity of fish species.