Due to the essential oils known as having great antimicrobial activities, they have been heavily used by several industries such as medical, cosmetics, food and agriculture since long past of human history. The essential oils are the secondary metabolite of aromatic plants and about 1/10th of known 3000 essential oils are widely used. They reached to the environment after used in any product and behave as xenobiotics especially in aquatic environment. Although, essential oils are natural plant extracts could be potential candidates for pest control or used any other purposes possible environmental impact needs to be investigation. In order to investigate the environmental impact of some essential oils such as rosemary oil, tea tree oil, wheat germ oil, grape seed oil, thyme oil and eucalyptus oil, Scenedesmus subspicatus were selected for testing as one of the primary producer species since they are the first trophic level of food chain. This test is approved as OECD 201 Algal Growth Inhibition test. As the result of this investigation, algal growth inhibition assays of tested oils did not show severe effects on the population growth of algae. The estimated EC50 values were 15.6, 35.09, 65.03, 100.17, 201.02, 414.47 mg/L for rosemary oil, wheat germ oil, tea tree oil, thyme oil, eucalyptus oil and grape seed oil respectively.