A seasonal variation study was performed on the chemical composition of the essential oil of Agathosma ovata (Rutaceae). In addition, this study looked at how variations may impact the antimicrobial activity of A. ovata. The chemical composition of 10 monthly samples, as determined by GC and GC/MS, were found to differ qualitatively and quantitatively and the analysis resulted in the identification of 144 compounds. Sabinene was the major compound in the oil and ranged between 25-44% over the year. The antimicrobial activity was evaluated using the minimum inhibitory concentration (MIC) method on four pathogens, i.e. Staphylococcus aureus, Bacillus cereus, Klebsiella pneumoniae and Candida albicans. Most of the samples had MIC values of 8 mg/mL. The activity for Staphylococcus aureus showed the greatest fluctuation (1.5-14 mg/mL) over the seasonal period.