Mastitis is the most important and and costly problems encountered in the farms. Sub-clinical stage of mastitis is especially dangerous. At this stage the milk seems normally and the udder or diseased area seems normally. But it effects milk production and milk quality continuing as sub-clinical and it can cause spreading infection among the other cows in the herd. Researches for many years revealed that an increase which reduced the electrical resistance of milk in the level of chlorine contained ions in the milk, causes the improvement of Mastitis. Electronic methods for test of sub clinic mastitis are commonly approved and used.