Epilepsy is a chronic neurodegenerative disease, and accumulating evidence suggests its pathological progression is closely associated with peroxynitrite (ONOO − ). However, understanding the function remains challenging due to a lack of in vivo imaging probes for ONOO − determination in epileptic brains. Here, the first near‐infrared imaging probe (named ONP) is presented for tracking endogenous ONOO − in brains of kainate‐induced epileptic seizures with high sensitivity and selectivity. Using this probe, the dynamic changes of endogenous ONOO − fluxes in epileptic brains are effectively monitored with excellent temporal and spatial resolution. In vivo visualization and in situ imaging of hippocampal regions clearly reveal that a higher concentration of ONOO − in the epileptic brains associates with severe neuronal damage and epileptogenesis; curcumin administration can eliminate excessively increased ONOO − , further effectively protecting neuronal cells. Moreover, by combining high‐content analysis and ONP, a high‐throughput screening method for antiepileptic inhibitors is constructed, which provides a rapid imaging/screening approach for understanding epilepsy pathology and accelerating antiseizure therapeutic discovery.