Self-assembled porous In₂O₃/ZnO heterostructures were prepared by a low temperature solution combustion synthesis method, and characterized using X-ray diffraction (XRD), scanning electron microscopy (SEM) and high resolution transmission electron microscopy (HRTEM). The results indicate that the as-synthesized porous In₂O₃/ZnO heterostructures were constructed from a large number of In₂O₃ and ZnO nanoparticles and showed high gas sensing performance toward Cl₂. Compared with pure ZnO and other heterostructure sensors, the porous In₂O₃/ZnO heterostructures with an appropriate molar ratio of In₂O₃ : ZnO exhibited highly enhanced gas sensing performances toward Cl₂. An extremely high sensitivity of 6610 could be reached when exposed to 50 ppm Cl₂ at 370 °C; also, In₂O₃/ZnO heterostructures showed high selectivity toward Cl₂. Furthermore, the gas sensing mechanism was discussed.