A thermal decomposition is proposed to convert a waste linear alkylbenzene sulfonate (LAS) into a solid material that is environmentally more favorable and disposable at a lower cost. The waste LAS is a viscous liquid containing sulfur as high as 13.3 wt %. The waste LAS was heated in a nitrogen atmosphere at 200-300 degrees C for 1-4 h. The thermal treatment at 250 degrees C for 2 h decomposed the waste into vapors and a solid material or residue, 2.0 wt % in sulfur content. The vapors were cooled with water to form two condensate layers in the receiving cylinder. The upper layer was identified to be a linear alkylbenzene (LAB) and the lower one a mixture of water and organic sulfur oxy compounds. The uncondensed vapor that left the condenser was determined to be a mixture of SO2, SO3, and H2SO4. A material balance shows that the mass of the waste LAS charged was distributed in the decomposition products as follows: the solid residue, 65.3%; the LAB, 5.6%; the mixture of water and organic sulfur compounds, 5.6%; the mixture of SO2, SO3, and H2SO4, 21.5%; unidentifiable loss, 2.0%.