In this study, natural sepiolite was employed as the support of TiO2 for improving the photocatalytic degradation activity for indoor formaldehyde (HCHO) under solar light. The various TiO2/sepiolite composites were prepared to investigate the effect of TiO2 loading amount and crystallization temperature on HCHO degradation performance. The composite with TiO2 loading amount of 50% and 500 °C exhibited the optimal performance, whose mineralization rate was up to around 2.63 times higher than that of pure TiO2. The performance enhancement mainly resulted from the uniform deposition of TiO2 with smaller grain size on sepiolite surface, leading to more exposed active sites, higher quantum efficiency and faster carrier separation efficiency. As a result, more active radicals were generated in composite thereby boosting the HCHO degradation performance. Overall, our study improve the understanding on the photocatalytic oxidation of HCHO by mineral-based photocatalyst, thereby promoting the practical application in indoor air purification.