Brucellosis is an infectious and contagious bacterial disease of animals and humans caused by Brucella .spp. In This survey, the brucella infection rate was studied in dairy cattle of industrial and non-industrial herds in Mazandaran province. 1200 milk specimens were randomly collected from whole 400,000 heads of cow in the area. It must be indicated that 600 samples of milk samples were taken from dairy cows of industrial farms and 600 samples of them from dairy cows of traditional herds. The specimens were collected from 3 regions in this province. Ring milk test were done on milk samples. The results showed that brucella infection in province was 2.66% for industrial farms, 8.66% for non-industrial herds and 5.66% for total cows of province (68 Reactor of 1200 samples). Generally according to the results of this survey, must be searched in other animals like sheep and goat.