One of the efforts to control the growth of microorganisms is sterilization. The sterilization process can use ozone gas, which is a triatomic form of the element oxygen. Ozone acts as an oxidizing agent capable of destroying the structure of bacterial cell walls, and their molecules are unstable and easily decomposed into oxygen, so that ozone can be applied in sterilization technology for medical devices. In this work, a sterilization box with an ozone generator has been designed with a MQ-131 ozone sensor as an indicator if there is a leak in the box. The output voltage of the ozone generator is 4 kV with a current of 30 mA. We developed an instrument using an Arduino nano as a microcontroller for reading sensor values and displaying sensor values on an LCD monitor. For testing the sterilization effect of the ozone box, a Staphylococcus aureus bacterial sample was used. For the sterilization object, we designated stethoscopes and thermometers as medical equipment. The optimum time for sterilizing medical devices on the sterilization ozone box was 20 minutes, which can reduce the colony of S. aureus bacteria with an ozone concentration of 4.94 ppm.