Abstract: Abstract: Whole milk contains plenty of nutrient elements, and it is regarded as "liquid gold". However, the adhesiveness of the elements makes them easily attach on the inner surface of milking system, which provides a good environment for microorganism growth. A mass of microorganisms can form a biofilm in the milking system, which is reported as a main contaminant of the system. Thereby, washing the milking system before and after milking the cows is a very important way to keep the milking system in a good hygiene condition, and beneficial to milk quality. In practical production of dairy farms, the traditional clean-in-place (CIP) process includes 4 steps: 1) Warm water rinsing; 2) Alkaline or acidic detergent cleaning circularly; 3) Warm water rinsing; and 4) Sanitizer or 90-95 ℃ hot water cleaning before next milking. In Step 2, chemical detergent with strong corrosivity is commonly used. Its residue may result in milk quality issue, and long term of usage is harmful to both the milking equipment and workers. Furthermore, the treatment of waste water containing detergent generated in the process is still a challenge, and its discharge may also present environmental risks. Thus, it is highly needed to find an alternative solution, which is more environmentally friendly and less harmful, to replace the traditional detergent. Electrolyzed water (EW), as an emerging, green and environment friendly detergent, has been widely applied in food industry and medical industry. Alkaline electrolyzed water (AlEW) and acidic electrolyzed water (AEW), with similar properties to the traditional alkaline and acidic detergent used in milking system, are promising options. Slightly acidic electrolyzed water (SAEW) with pH value ranging from 5.5 to 6.5, was considered in this study because of its low corrosivity and high bactericidal activity compared with AEW. Aiming at finding an optimal mode of using AlEW and SAEW in cleaning milk tank, and reducing cleaning costs, this study tested the effect of using AlEW with the parameters of 8 min treatment time, 70.3 ℃ cleaning temperature and pH value of 12, as well as SAEW under the condition of 9.9 min treatment time, 37.8 ℃ cleaning temperature, and available chlorine concentration of 60 mg/L to clean a 100 L milk tank. The modes were set as "AlEW for one time + SAEW for one time" (cleaning the tank with AlEW in the first time and then with SAEW in the second time), "AlEW for 2 times + SAEW for one time" (cleaning with AlEW for 2 times and then with SAEW in a third time) and "AlEW for 3 times + SAEW for one time" (cleaning with AlEW for 3 times and then with SAEW in a fourth time). Cleaning effect of electrolyzed water was compared with that of commercial detergent (Super, DeLaval Co. Ltd., Tianjin, China), following the manufacture's recommendation of using "alkaline detergent for 2 times + acidic detergent for one time" mode. Results showed that both AlEW and SAEW were highly efficient in removing microorganism and ATP (adenosine triphosphate) in the milk tank, and the removing rates were comparable or better than that of commercially used detergent (Super), indicating their potential in cleaning and disinfecting of milking system. Based on cleaning effect and costs, the mode of "AlEW for one time + SAEW for one time" was recommended. Field experiment of using AlEW and SAEW in commercial dairy farm is suggested, and its application is expected in the future.