The present study deals with the safety evaluation of thyme essential oil used as a spice in foods on liver and kidney functions of rats. Therefore, the activities of some enzymes of rat plasma, i.e., alanine aminotransferase (ALT), aspartate aminotransferase (AST), and alkaline phosphatase (ALP) as well as rat plasma contents, i.e., total triglycerides, total cholesterol, LDL- cholesterol, HDL- cholesterol, urea, uric acid and creatinine were determined for rats administered with thyme essential oil at two concentrations of 200 and 400 ppm. In addition, histopathological examinations were performed in order to emphasis the results of biochemical determinations of liver and kidney functions. In general, the thyme essential oil induced little changes in aminotransferases activity in rat plasma and desirable changes in total cholesterol, LDL- cholesterol and HDL- cholesterol. On the contrary, this oil did not induce any changes in urea, uric acid and creatinine contents. Histological examination showed no changes in kidneys and liver tissues, except hydropic degeneration of some hepatocytes. So, the essential oil induced limited alteration in some parameters relevant to liver and kidneys functions. The outcome from these results that the essential oil of aerial part of thyme plant had harmless effect on liver and kidneys tissues.