In this work, we successfully prepare the octahedral NiO/Zn2SnO4 p-n heterostructure by a simple hydrothermal synthesis and subsequent wet impregnation process. The microscopic morphology characterization results show that the as-prepared composites are uniformly dispersed and have an octahedral structure with a size of 3-5 ?m. The gas devices are fabricated and their sensing performances are investigated systematically. The response and selectivity of NiO/Zn2SnO4 composites to acetone have been significantly improved than that of pure Zn2SnO4. Moreover, the response of the sensor to 100 ppb acetone is 1.4 at 300 ?C, indicating that the detection limit is less than 100 ppb. The enhancement in sensing properties of composites is largely due to the p-n heterojunction formed by NiO and Zn2SnO4, which causes the transfer of carriers and the catalytic effect of NiO