AMP-activated protein kinase (AMPK) is the master regulator of cellular and organismal energy homeostasis, playing an essential role in modulating metabolism and other cellular processes. Substantial efforts have been made to develop pharmacological modulators of AMPK activity due to their therapeutic potential against various diseases. Measuring AMPK activity in vitro is a fundamental step for testing AMPK activators and inhibitors. Here, we report an enzyme-linked immunosorbent assay (ELISA)-based AMPK activity assay with simple steps and high sensitivity. This assay offers a robust, in-house alternative to the traditional radioactive methods and other approaches that rely on specialized reagents or commercial kits.