Epilepsy is considered one of the most prevalent neurological disorders, yet the precise mechanisms underlying its pathogenesis remain inadequately elucidated. Emerging evidence implicates endogenous sulfur dioxide (SO₂) in the brain as playing a significant role in epilepsy and associated neuronal apoptosis. Consequently, tracking the dynamic fluctuations in the levels of SO₂ and its derivatives (SO₃²⁻/HSO₃⁻) provides valuable insights into the molecular mechanisms underlying epilepsy, with potential implications for its diagnosis and therapeutic intervention. Nonetheless, the absence of reversible in vivo detection tools constitutes a formidable obstacle in the real-time monitoring of SO₂ dynamics in the brain. In response to this challenge, we propose a novel approach involving a photoelectrochemical (PEC) microsensor capable of reversibly detecting SO₂. This microsensor leverages a reversibly recognizing dye for SO₂ and upconversion nanoparticles as the modulator of the excitation source for the photoactive material, enabling modulation of the photocurrent by the target. The reversible output of PEC signals allows for the monitoring of SO₂ levels in real time in the brains of epileptic mice. This study reveals the patterns of SO₂ level changes during epilepsy and provides insights into the neuroprotective mechanism of exogenous SO₂.