Indoor air quality detection, especially formaldehyde (HCHO) detection, is of great importance in practical application. A key limitation of promoting gas-sensing devices is the lack of sensing materials with high sensing sensitivity and selectivity. In this study, SnO₂ mesoporous nanoparticles are fabricated by a facile hydrothermal route with a subsequent acid etching process. The prepared samples show high response toward HCHO (133.5, 222.8 for 100 ppm and 200 ppm HCHO, respectively) and short response/recovery time (15/22 s at 10 ppm). The excellent HCHO sensing performance benefits from the comprehensive regulation of the depletion region width, surface area and rich porosity, which is effective for the promotion of surface adsorption and catalyst activity. It is expected that the excellent sensing properties are promising for practical HCHO gas detection.