A rapid and sensitive cataluminescence (CTL)-based gas sensor using nanosized V2Ti4O13 as a probe was proposed for the determination of formaldehyde in air. The gas sensor showed high selectivity for formaldehyde at 490 nm and satisfying activity at 370 °C. The linear range of the CTL intensity versus concentration of formaldehyde was 0.1–40 mg/m3 (γ = 0.9995), and the detection limit (3σ) was 0.06 mg/m3. No interference was observed while the foreign substances, such as ammonia, ethanol, benzene, carbon monoxide and sulfur dioxide, were passing through the sensor. The gas sensor displayed good stability for continuously introducing formaldehyde over 80 h, and allowed on-line monitoring of formaldehyde in air.