Rosemary (Rosmarinus officinalis L.) is a spontaneous shrub growing in all Mediterranean countries. Different species of rosemary exist all over the world: R. officinalis, R. erriocaly, R. laxiflorus and R. lavandulaceus. R. officinalis is the only one that grows naturally in the Mediterranean regions. Other studies reported that the differences between plants and oils composition were correlated to the differences of the substrate. In this work plant material of 87 spontaneous populations of R. officinalis were collected in the Spanish regions of Andalucía, Aragon, Baleares, Castilla-La Mancha, Cataluña, Madrid, Murcia and Valencia. The composition and chemical polymorphism of the essential oils were analysed by GC. The results obtained in a water distillation of volatile oils, were submitted to a multiple regression analysis which showed a negative significant correlation between the concentration of essential oil and the altitude with ap< 0.05. Among all samples, 38 of them had high 1.8-cineol (> 24%) content and high yield of essential oil (> 2%), 6 of them showed high 1.8-cineol/linalool and 3 samples had high linalol content. Two samples from Andalucia gave high content in verbenona (5.49, 5.37%)