The process of filling milk in bottles in small and medium industries is still done manually with human labor, so the operator must pay attention to the volume of milk and takes a long time. This Arduino uno-based liquid fluid filling designer is supported by the Water Flow yf-S201 sensor to read the flow of water. The purpose of this research is to find out the working system of the liquid fluid filling device in an automatic bottle based on Arduino Uno. The research conducted uses a procedural development model. The results showed that filling milk into bottles manually takes ± 340 seconds in 1 bottle filling. If using an automatic bottle filling tool based on Arduino Uno Microcontroller and Flow sensor the filling process on 1 bottle takes ± 210 seconds. This tool still has weaknesses, the weakness of this tool in filling the 5th bottle the volume drops compared to the previous bottle.