In the present work, gas sensing properties of the screen printed ceria and ruthenate-sensitized BaSnO₃ (BSO) with La doping heterostructure sensors towards the detection of ammonia and formaldehyde gases at room temperature were studied. Adhered, porous screen printed films with different morphologies were obtained by depositing the La_xBa_1−xSnO_3−δ (x = 0 and 0.05) powder particles prepared by the polymerized complex method. Ceria and ruthenate sensitization for screen printed La_xBa_1−xSnO_3−δ (x = 0.05) film was processed through dip-coating in the 0.03 M aqueous solution of CeCl₃ and RuCl₃, respectively. La-doped BaSnO₃ (LBSO) sensor with smaller crystallites, needle-like morphology and high concentration of oxygen vacancies exhibited superior gas response of 65 and 29 towards 50 ppm of ammonia and formaldehyde gases, respectively. Superabundant sensitization of ceria and ruthenate reduced the oxygen vacancy and structural open porosity in the LBSO sensor; therefore, the ammonia gas response was decreased from 65 to 14 and 3, respectively, whereas the formaldehyde gas response was reduced to less than 1/6th times the LBSO sensor. Limit of detection of LBSO sensors was estimated to be ~ 1 and ~ 2 ppm against ammonia and formaldehyde, respectively. The presence of fluorite structured phase ceria with high oxygen atoms storage capacity facilitates the rapid oxidization of analyte gases and caused the expeditious response (75 s) and recovery (60 s) in CeO_x-sensitized LBSO sensor. This study might give a new insight into the development of doped and sensitized BSO-based gas sensors operating at ambient conditions.