Understanding the photocatalytic conversion mechanism of NO is crucial to develop an effective and practical strategy for indoor air pollution control. In this study, we systematically investigated the photocatalytic removal mechanism of NO over nanocrystalline Bi₂Sn₂O₇, which was successfully synthesized via hydrothermal method using bismuth citrate and stannic chloride pentahydrate as precursors for the first time. Various characterizations were carried out to study the physicochemical properties of the as-prepared samples. The performance of the as-prepared Bi₂Sn₂O₇ samples was evaluated by the photocatalytic degradation of NO in a continuous reactor under simulated solar light irradiation. The NO removal rate over the Bi₂Sn₂O₇ sample synthesized for 12 h (BSO-12) was 37%, which was much higher than those of Bi₂Sn₂O₇ samples synthesized for 24 h (BSO-24) and 36 h (BSO-36). Results from photocurrent tests and electrochemical impedance spectroscopy (EIS) demonstrated that the BSO-12 sample presents much more effective interface charge separation efficiency, which can contribute to its improved photocatalytic performance. Reactive radicals during the photocatalysis processes were identified via trapping experiments, which were also confirmed by electron spin resonance (ESR) study. Combined with the quantification of reaction intermediates, the photocatalytic removal mechanism of NO over nanocrystalline Bi₂Sn₂O₇ was proposed for the first time. Copyright © 2016 American Chemical Society.