Thymol shows potential medical values and it can be extracted from plants and herbs. In this study, ultrasonic-assisted extraction (UAE) was used to extract thymol from Plectranthus amboinicus leaves. From the extraction kinetics analysis of UAE on thymol, it was found that the highest concentration was collected at temperature of 25 °C with 5.51% of thymol concentration yield. An equilibrium-dependent solid−liquid extraction (EDSLE) model was found to be the best fitted model for thymol extraction using UAE. The parameters for optimization were the temperature of extraction (40 to 60 °C), extraction time (20 to 40 min), and the solid to solvent ratio (1:30 to 1:40 g/mL). The optimal UAE conditions were found at a temperature of 55 °C, 23 min of extraction, and a solid−solvent ratio of 1:35 g/mL. The changes in the structural surface of P. amboinicus after undergoing the UAE process were investigated using scanning electron microscopy (SEM). The possible mechanism of UAE was explained using the SEM images. These findings suggest that UAE is capable of breaking the structural surface of the leaves to extract compounds inside the leaves to the body of the solvent.