The essential-oil composition of 60 individual trees of Juniperus phoenicea L. from four Tunisian populations in three different periods were investigated by GC and GC/MS analyses. 59 Compounds were identified in the oils, and a relatively high variation in their contents was found. All the oils were dominated by the terpenic hydrocarbon fraction, and the main component was alpha-pinene (20.28-40.86%). The results of the oil compositions were processed by hierarchical clustering and principal component analysis (PCA) allowing establishing four groups of essential-oils differentiated by one compound or more. Pattern of geographic variation in essential-oil composition indicated that individuals from the continental site (Makthar) were clearly distinguished from those from littoral localities (Tabarka, Hawaria, and Rimel).