A two-step route was used to prepare SnO2/ZnO composite hetero-nanofibers. In the first step, hierarchical SnO2 nanofibers were synthesized by electrospinning; in the second step, ZnO nanospheres were fabricated in zinc acetate solution using water bath at 90 degrees C. The morphology, structure and composition of SnO2/ZnO composite hetero-nanofibers were characterized and analyzed by XRD, SEM, EDX, and XPS. SnO2 nanofibers in the composite materials keep hollow and hierarchical structure with 300 nm in diameter. The diameters of ZnO nanospheres grown on SnO2 nanofibers are 250-300 nm. Gas sensing properties of SnO2/ZnO composite hetero-nanofibers were tested using a static gas testing system. Gas sensing properties of pure SnO2 nanofibers and ZnO nanospheres were also studied to compare their gas sensing properties. The results show that SnO2/ZnO composite hetero-nanofiber gas sensors exhibit excellent sensing sensitivity, selectivity and long-tern stability for (0.5-100)x10(-6) acetone at 350 degrees C N-N homotype heterojunctions, existed in the joint between ZnO nanospheres and SnO2 particles in the SnO2/ZnO composite materials, change the potential barrier height. The absorption capacity of SnO2/ZnO composite materials increases greatly due to changes of the transport characteristics of electrons and holes, which results in the improvement of acetone sensing properties of SnO2/ZnO composite materials.