The aim of this study was to determine the antifungal in vitro activity of rosemary oil (Rosmarinus officinalis) against Microsporum canis. A strain of M. canis was isolated from clinical samples. The rosemary oil was obtained by the method of steam distillation with a purity of 100%. By the well diffusion method the strain of M. canis was faced against eight concentrations of rosemary oil (250, 500, 1000, 2000, 5000, 10 000, 50 000 and 100 000 ppm). The results showed an adequate sensitivity of M. canis at a concentration of 50 000 ppm onwards.