In this work Rosmarinus officinalis L. grown in Syria was studied. The general characteristics of the whole plant, as well as the leaves and the flowers were determined. It was shown that there are two varieties of Rosmarinus one having violet flowers and the other having white flowers. The two varieties were compared morphologically and they were in accord with what was mentioned in the literature. The two varieties were also compared chemically and it was possible to explain the differences mentioned in the literature by differences in the composition of the volatile oil. The chemical study of the drug shows the quantity as well as the percentage of its constituents. At last the main substitute of the drug used in Syria was shown and compared with the main drug. It was shown that the composition of the volatile oil of the substitute is different from the composition of the volatile oil of Rosmarinus, thus it can not be used for the same purpose.