Chemical composition of the essential oil of Ocimum basilicum L., O. gratissimum L. and O. americanum L. varieties found in Sierra Leone and Nigeria were determined by GC-FID and GC-MS. The antimicrobial test was evaluated by agar diffusion. The Sierra Leone and Nigeria O. americanum L. varieties were identified as the linalool chemotype and similarly, varieties of O. gratissimum L. from both countries are thymol chemotype. The high thymol content is consistent with the relative high antimicrobial activity of the O. gratissimum L oils. The Sierra Leone O. basilicum L. sample was established as the methyl eugenol chemotype while the Nigerian collection is predominantly methyl chavicol in composition. The high methyl eugenol content of the Sierra Leone collection is consistent with the observation of attraction of fruit flies to the distillate. To the best of our knowledge, there has been no report on essential oils of Ocimum species in Sierra Leone, hitherto.