Club root disease is one of the most important diseases in Cruciferae family which causes the formation of galls on the roots. These galls are different in size and include small knots to club-shaped large tumors which occupy a large part of the root system. This disease is one of the major diseases in Europe, the United States, Canada and New Zealand. Up to now, this disease is regarded as a quarantine disease in Iran. During 1396-1397, with the aim of the identification of canola root rots in Khuzestan province, a lot of canola root samples were collected from different townships including Ahvaz, Andimeshk, Omidiyeh, Izeh, Bavi, Behbahan, Jayzan, Khoramshahr, Darkhoveyn, Dezfool, Soosangerd, Shadegan, Shoosh, Shooshtar, Gotevand, Masjedsoleyman and Lali. Among these, five samples were infected to club root disease and displayed little hypertrophy in cortical cells. Collected samples were packed into paper bags and transferred to the lab. roots were washed with distilled water in the lab, and then, thin sections of the infected roots were prepared. These sections were stained with captain blue,for about 5 hours. Than microscopic slides were prepared from samples. Observing samples with microscope indicated that infected roots occupied with the secondary plasmodiumes, and that, these secondary plasmodiumes were full of sporangium these sporangia have a different sizes from 3.43 micro meter to 8.86 micro meter (50 sporangium) with the average of 6.37 micro meter. compaiving these data with the mycological stsndard keys, the cause of canola club root was determined as plasmodiophora brassica. this is the first report of occurving of club root disease in canola plant in Iran.