Dadap serep leaves (Erythrina subumbrans (Hassk.) Merr) contained saponins, flavonoids, tannins, and alkaloids which had the potential to lower body temperature. This research aimed to formulate a stable transdermal patch of Dadap Serep Leaf Extract (EDDS) and evaluate this transdermal patch based on temperature changes in white mice (Mus musculus) hyperthermia models at 17, 20, and 40%. This research was an experimental laboratory with a pre- and post-test control group design to test the effectiveness of the EDDS transdermal patch. Evaluation of the patch used physical quality stability tests using the freeze-thaw method including organoleptic, weight uniformity, thickness, folding resistance, and pH. Then the effectiveness test of this EDDS transdermal patch was tested on a white mouse hyperthermia model. The treatment group consisted of positive control (marketed compress product), negative control (peptone induction), and transdermal patch with EDDS extract at 17, 20, and 40% for 2 hours with monitoring every 30 minutes. The results showed that the transdermal patch preparation had good stability after physical quality stability testing using the freeze-thaw method. It was concluded that the most effective EDDS transdermal patch formulation in reducing temperature in white mice was a concentration of 40% with a temperature reduction percentage of 84.5%. Keywords: Transdermal Patch, Hipertermia, Dadap Serep Leaves, Soxhletation, Freeze-thaw