This study investigated the in vivo antimicrobial activity of the essential oils of Origanum vulgare and Mentha piperita both singly, associated and in combination with immunotherapy to treat experimental pythiosis. The disease was reproduced in 18 rabbits divided into six groups (n=3): group 1, control; group 2, treated with essential oil of Mentha piperita; group 3, treated with essential oil of Origanum vulgare; group 4, treated with commercial immunotherapic; group 5, treated with a association of oils of M. piperita and O. vulgare and group 6, treated with a combination of both oils plus immunotherapy. Essential oils were added in a topical cream base formula, and lesions were treated daily for 45 days. The animals in groups 4 and 6 received a dose of immunotherapeutic agent every 14 days. The results revealed that the evolution of lesions in groups 5 and 6 did not differ from one another but differed from the other groups. The lesions of group 5 increased times every measurement, while those of group 6 increased times, indicating that the smallest growth of the lesions occurred when the combination of therapies were used. A rabbit from group 5 showed clinical cure at day 20 of treatment. This research is the pioneer in the treatment of experimental pythiosis using essential oils from medicinal plants and a combination of therapies. This study demonstrated that the use of essential oils can be a viable alternative treatment to cutaneous pythiosis, particularly when used in association or combination with immunotherapy.