The present study was carried out with Epilithic diatoms collected from rocky lithophytes on the Rasthakadu coast, Kanyakumari district. Numerous diatoms are adhesive to lithophytes. Diatom is a key component of marine ecosystems. Algal biomass and diatom species composition were good indicators of nutrient enrichment. Epilithic diatoms were all good biological indicators and also nutrient enrichment to industries that produce some cosmetic items in lithophytes. Marine ecosystem mixed with some industrial wastes; environmental condition produces changes in Diatoms populations. Species composition is often affected by climatic and spatial variables. The present work identified 44 diatom species and analyzed their adhesive strength, and composition, with the lithophytes. Also, the nature, and structure of diatoms and to understand the role of diatoms in the Rasthakadu marine ecosystem. To record the needed measures to be undertaken to protect the present epilithic diatoms.