A simple and cheap flexible gas sensor utilizing polyaniline @ porous nanosphere SnO2/Zn2SnO4 nanohybrid (PZN) was assembled on a polyethylene terephthalate (PET) film free of interdigital electrode by in-situ chemical oxidation polymerization technique for rapid and selective detection of NH3 at room temperature. The structure, morphology and composition of as-prepared sample was characterized roundly through XRD, FESEM, TEM, Raman, UV-vis and XPS, respectively. The effect of different mole amount of porous nanosphere SnO₂/Zn₂SnO₄composite on NH₃sensing response was appraised and the results indicated that PZN flexible sensor with a 10 mol% porous nanosphere SnO₂/Zn₂SnO₄(PZN 10) to 100 ppm NH3 exhibited response signal of 20.4, which is 2.6 times higher than that of pristine polyaniline (7.8) at room temperature. Furthermore, PZN 10 flexible sensor possessed low detection limit of 500 ppb of NH₃in conjunction with good reproducibility, bending and robustness properties at room temperature. The enhanced NH₃sensing properties can be attributed to the morphology structure and p-n heterojunction between polyaniline and porous nanosphere SnO₂/Zn₂SnO₄, and the underlying sensing mechanism was also further analyzed and verified using impedance spectroscopy.