A fiber optic toxic gas sensor with modified cladding region coated with a sensing material of TiO2nonmaterial has been proposed in this work. The change in refractive index of the cladding and the phenomenon of evanescent wave absorption are used in the sensing principle here, to study the sensitivity towards toxic gases(acetone, isopropyl alcohol and benzene). The intensity variation is maximum at the wavelengths of 641.42 nm and 756.76 nm for and hence shows good sensitivity towards toxic gases. The sensor has been used for detection of toxic gases such as acetone. As-prepared and annealed(500 °C,1200 °C)samples were used as gas sensing media.The average particle size characterized from powder X-ray diffraction (XRD) was found to be around 13,16 &21 nm for as-prepared and annealed TiO2nanomaterials respectively. The spectral characteristics of the fiber optic gas sensorare studied for various concentrations of toxic gases (0–500 ppmin steps of 50 ppm). The sensor exhibits linear variation in the spectral peak intensity with the acetone concentration. The characteristics of the sensor with benzene and isopropyl alcohol gases are also studied for gas selectivity. The time response characteristics of the sensor are reported. © 2015, Sphinx Knowledge House. All rights reserved.