Navicula sp is one of the microalgae which plays an important role in fish and shrimp hatchery activities. Navicula sp. which can detect the surrounding environment and is able to adapt to various salinities. The purpose of this study was to determine the optimal salinity level for the growth of Navicula sp. The research was carried out on March 9 - 22 2022. The research location was carried out at the Natural Feed Laboratory of the Brackish Water Aquaculture Fishery Center (BPBAP) Ujung Batee Province of Aceh. This study used an experimental method with a completely randomized design (CRD), with 4 treatments and 3 replications. The treatment in this study is the difference in salinity: A (10 g/l), B (20 g/l), C (30 g/l), D (40 g/l). The results showed that treatment B with a salinity of 20 g/l had a significant effect (P <.0.05) on the other treatments. The results of the Duncan Significant Difference Test showed that the maintenance medium with a salinity of 20 g/l had the highest cell density (5.63x106 cells/ml), followed by the maintenance medium with a salinity of 30 g/l with a cell density (5.20x106 cells/ml).