Dielectric Behaviour of Thiophenol in Benzene, Carbon tetrachloride, Cyclohexane, n-hexane. R.S. Kawale a , U.B. Tumberphale b , V.G. Kalamse b and G.M. Kalamse b *. “Dept. of Electronics, D.S.M. College, Jintur, Dist. Parbhani – 431509, Maharashtra INDIA “Dept of Physics, N.E.S. Science College, NANDED – 431605, Maharashtra INDIA Emial : ravi.kawale1972@gmail.com ABSTRACT : Using Surber’s technique of measuring reflection coefficient from the air- dielectric boundary of liquid, the dielectric constant (ε′), dielectric loss (ε″) of Thiophenol with benzene, carbon tetrachloride, cyclohexane, n-hexane and their binary mixtures for different mole fraction of thiophenol have been estimated at 15.2 GHz microwave frequency at 30 0 C. The values of loss tangent (tan), molar polarization (P 12 ) and dipole-moment (μ), of binary mixtures as well those of pure liquids are reported. Keywords : Dielectric parameters, polarization, dipole moment, binary mixture, complex formation. Introduction:- Thiophenol (Phenyl Mercaptan (C 6 H 5 SH) is used as an intermediate in the manufacture of pesticides, pharmaceuticals and amber dyes and is also used as a mosquito larvicides. It is an odorous, colourless liquid. The disagreeable odour has been described as penetrating, repulsive and garlic like. Phenyl Mercaptan depresses the central nervous system and affects the respiratory centre,similar to hydrogen sulfide, producing death by respiratory paralysis.Clinical signs of exposure are eye and mucous membrane irritation ,headache, dizziness, staggering gait, nausea and vomiting. Paralysis of the locomotor muscles has also been observed (Wikipedia). Experimental investigation of dielectric properties of organic compounds is of great value in understanding the nature of complex formation between the molecules.The knowledge of dielectric properties of organic compounds and their mixtures at microwave frequencies helps in their characterization and applications (Kalamse et al 2002). During literature review, the author came to know that thiophenol (Phenyl Mercaptan) due to its toxicity remains untouch.