Macroporous SnO₂ films mixed with 2.5 mol% Eu₂O₃ and n mol% MgO (mp-Eu₂O₃/SnO₂(nMgO)) were fabricated by a modified sol-gel technique employing polymethylmethacrylate microspheres (ca. 800 nm in diameter) as a template, and their photoluminescence (PL) intensities under various gaseous atmospheric conditions and gas-response behavior were investigated under the UV-light irradiation (wavelength: 260 nm) at a room temperature of ca. 25 °C. The PL intensities of the mp-Eu₂O₃/SnO₂(nMgO) films were largely dependent on the mixing amount of MgO, n, and they showed the largest PL intensities at n ═ 10-20. The existence of well-developed macropores in the films largely improved the response properties to some target gases. Namely, the responses of the mp-Eu₂O₃/SnO₂(nMgO) sensors to 5-50% O₂ in N₂ and 8000 ppm H₂ in air was much larger than that of conventional Eu₂O₃/SnO₂(nMgO) sensors without such macropores, which were fabricated by screen printing. The mp-Eu₂O₃/SnO₂(nMgO) sensors also obviously showed large responses to 2% H₂O and 3-60 ppm NO₂ in air. In addition, their PL intensities increased after the addition of O₂ into N₂, H₂O in air, and NO₂ in air, while they decreased after the addition of H2 in air. These results indicate that the componential change in gaseous atmosphere has a great influence on the effective energy transfer from the SnO₂ host to Eu3+, especially at the oxide surface, to control the PL intensity of these Eu₂O₃/SnO₂(nMgO) films.