Hypoxanthine is a well-known indicator of intracellular energy status that is associated with many pathological conditions. We report a fluorescent luminogen (TPE-HPro) with aggregation-induced emission (AIE) feature which, along with xanthine oxidase (XO), detects and quantifies hypoxanthine in a "turn-on" manner. The superior detection performance of this fluorometric assay indicates its great potential for biomedical diagnostics.