In the present report, an enhanced sub-ppm level acetone sensing performance of a novel Pt and Sb2O3 impregnated nanocrystalline Fe2O3 thin film operating at room temperature has been explored. Starting from organic precursor sols, thin films of thickness ~ 6 µm were drop-casted on planar alumina substrates pre-attached with the platinum electrodes and cured at ~ 350°C. The characterizations of the materials have been carried out using X-ray Diffraction, FTIR, Raman Spectroscopy, micro structural study through FESEM and TEM as well as XPS analyses. The sensing characteristics including sensing response, lowest detection limit, recovery time etc. of these chemiresistive thin films were studied on exposing them to various concentrations (0.25 to 1 ppm) of acetone at room temperature. The sensing response of ~2.4 with ~ 95 s recovery time was observed on exposure to 1 ppm acetone for 10 s. Even at 0.25 ppm acetone, the response observed ~ 1.4. Selectivity study on different alcohols and other interfering gases of breath has also been tested. Additionally, a real time breath acetone measurement was carried out and acetone sensing mechanism has been elucidated.