Abstract Variation on chemical composition of essential oils produced from Ocimum micranthum Willd. obtained from plants growing in northeast Brazil, at different stages of development and throughout the day. The oils, which were obtained by microwave oven distillation, were analyzed by GC/MS. A discreet variation in the eugenol contents from 97% at 6:00 a.m. to 84% at 6:00 p.m. was observed. The highest value was found in oil obtained from a specimen with a fully developed inflorescence. The eugenol production in O. micranthum does not appear to be influenced by solar light throughout the day.