Fruit juice may function as functional drink to improve human immune system. Fresh fruit-based functional drink contains high number of bioactive compounds, but it also may contain harmful microorganisms. The first objective of this work was to study the effect of ultrasonic amplitude and processing time on the microbial content and antioxidant activities of novel black mulberry-pineapple-mango functional drink. The second objective was to optimise the ultrasonic processing condition of the juice. Ultrasonic method was chosen in this study because it is a non-thermal processing technique which requires less energy consumption with shorter processing time. The study was conducted using Response Surface Methodology with ultrasonic amplitude (50 to 100 %) and processing time (4 to 12 min) as the investigated factors. The results show that ultrasonic treatment was able to reduce the microbial content yet maintained the antioxidant properties of the juice. The microbial content was significantly (p < 0.05) decreased, total phenolic content (TPC) and antioxidant activities (DPPH scavenging and FRAP) were significantly increased (p < 0.05) when high amplitude was applied. Increasing the processing time beyond 8.00 min was shown to cause negative impact towards total phenolic content and antioxidant activities of the drink. From optimisation, the best sonication condition for obtaining black mulberry-pineapple-mango functional drink with the lowest microbial content of 0.002 CFU/ml and highest TPC of 632.54 mg GAE/100 g, DPPH scavenging activity of 92.81 % and FRAP of 0.5127 mmol Fe2+/100 g is at amplitude of 100 % and processing time of 8.00 min. From the study, it can be concluded that ultrasonic processing is a potential alternative for fruit-based functional drink pasteurization.