An optical sensor for the dual sensing of oxygen (O2) and carbon dioxide (CO2) based on sensing films coated on filter paper is proposed. Ethyl cellulose (EC) doped with platinum(II) meso-tetrakis(pentafluorophenyl)porphyrin (PtTFPP) and 7-amino-4-trifluoromethyl coumarin serve as the oxygen sensing material and reference blue emission dye for the pH indicator, respectively. The CO2 sensing layer includes the pH-sensitive fluorescent indicator 1-hydroxy-3,6,8-pyrenetrisulfonic acid trisodium salt immobilized within the EC. The O2- and CO2-sensitive materials can both be excited with a 405 nm LED, and the two emission wavelengths can be detected separately. The experimental result reveals that the optical O2 and CO2 sensors have sensitivities of IN2 /I100%O2 =22.8 and IN2 /I100%CO2 =3.6, respectively. The response times of the optical O2 sensor were 15 s upon switching from nitrogen to O2 and 41 s when moving from O2 to nitrogen (N2). The response times of the optical CO2 sensor were 7 s upon switching from 100% N2 to 100% CO2 and 39 s when moving from 100% CO2 to 100% N2. The proposed optical dual sensor can be used for the simultaneous sensing of O2 and CO2 concentrations in environmental applications.