As a representative compound of cyclic sulfides, tetrahydrothiophene in different solvents was thermally decomposed under several high temperatures in a microreactor. The observed sulfur-containing product distribution reveals that the solvent used has a large effect on the sulfur distribution. When benzene was the solvent, dihydrothiophene, thiophene, and hydrogen sulfide were the main sulfur compounds produced in the decomposition process. However, only hydrogen sulfide was the main product when tetrahydrothiophene in tetralin was thermally decomposed. 1,3-Butadiene is the significant component among all of the hydrocarbons produced. Plausible decomposition pathways leading to the observed products were investigated by quantum mechanical calculations using the B3LYP density functional theory for geometry optimization and QCISD(T) for energy evaluation. On the basis of the calculated results, favorable decomposition pathways were proposed.