ABSTRACT: The semiarid region of Brazil holds a great richness of medicinal and aromatic plants with considerable potential for pharmaceutical, food, cosmetic and biopesticide industries. Martianthus leucocephalus (Mart. Ex Benth.) J. F. B. Pastore is endemic to this region, and its essential oils contain a principle compound, isobornyl formate, which demonstrates antimicrobial activity against Bacilus cereus, Staphylococcus aureus and Candida albicans. In spite of its significant pharmacological potential, little is known about its growth. In light of the influence of seasonality on plant growth, development, and secondary metabolism, the present study evaluated the growth and essential oil content of M. leucocephalus grown and harvested during different months of the year in the edaphoclimatic conditions of Feira de Santana, Bahia State, Brazil. The experimental design was entirely randomized, with twelve harvesting periods and five replicates. The study acquired monthly data of mean temperatures, relative humidity, rainfall, irradiance, and photoperiod from the National Institute of Meteorology (INMET) and quantified the fresh and dry weights of leaves, flowers and branches, as well as leaf area, and essential oil content. The data were submitted to Spearman correlation analysis and the means were compared using the Scott-Knott test. Total leaf masses and oil contents were higher during periods with longer photoperiods and higher solar irradiance. Rainfall and relative humidity reduced plant growth and essential oil content. Higher total mean dry masses were recorded from September to January (except October), while oil content was higher in March.