Combination of ozone and ultrasonic cavitation can use as an alternative process for disinfection of Escherichia coli where the residual of this process was considered to be more safety than the previous one (e.g. Chlorination). Ozone can attack membrane cell of bacteria and also ultrasonic cavitation has an advantage in the generation of OH radicals which make an enzyme denaturation on bacteria. This research divided into three kinds of disinfection method to find the best applicable one, which is disinfection using ozone, ultrasonic cavitation and combination of ozone and ultrasonic cavitation. The best condition for Escherichia coli disinfection resulted from this research was when a combination of 231 mg/L of ozone and 100% wave intensity used. This condition gave a result of 99.99% percentage of Escherichia coli disinfection in 15 minutes. Therefore, this research showed that combining ozone and ultrasound cavitation will effectively increase the disinfection capability of the process.