Zinc oxide nanorods decorated with gold nanoparticles were deposited on an optical fiber and were used for carbon dioxide gas detection at room temperature. This optical gas sensor is based on the changes in the intensity of transmitted light due to the interaction of gas molecules with zinc oxide surface. Zinc oxide nanorods were prepared by ultrasonic method and were decorated with spheroidal 20 nm gold nanoparticles. Sensing experiments were carried out using two different wavelengths. The sensor can respond to a CO2 atmosphere and recover to its original state once the gas is removed, showing a better response when red light is used. Moreover, it responds almost linearly with concentration until 2000 sccm. The incorporation of gold nanoparticles greatly reduces the sensitivity of the sensor and increases its recovery time. Preliminary results demonstrate that the sensor could also be used to sense vapors of common solvents.