Ultra-small Pt nanoparticles functionalized In₂O₃nanofibers have been designed by using a new catalyst loading platform (Pt@ZIF-8), which involves three steps including the synthesis of ZIF-8 nanoparticles, the preparation of Pt@ZIF-8 and the subsequent transformation to Pt-ZnO-In₂O₃composite nanofibers by electrospinning. The experimental results demonstrate that the average sizes of Pt nanoparticles obtained in this way are only similar to 3 nm, which is helpful to obtain highly sensitive gas sensors due to the ultra-small Pt nanoparticles. Gas sensing investigations indicate that the sensor based on Pt- ZnO-In₂O₃nanofibers exhibit the superior acetone response (R-a/R-g= 57.1 to 100 ppm at 300℃), ultra-fast response and recovery time (1/44s) and low detection limit (0.5 ppm). In this study, the excellent acetone gas sensing property of Pt-ZnO-In₂O₃nanofibers attributes to the chemical sensitization and electrical sensitization of the ultra- small Pt nanoparticles, the n- n heterojunctions between ZnO and In₂O₃, and the p-n heterojunction produced between p- type PtO₂and n- type In₂O₃( ZnO).