The theoretical study of the reaction between the hydroxyl (OH) radical and the methanethiol (CH3SH) presents some exciting points: i) A full-dimensional potential energy surface is not available for this gas-phase reaction; ii) Its interest in tropospheric chemistry, related with adverse effects, such as acid rain, climate changes or visibility reduction. Thus, the reaction with OH represents one of its important sinks in the atmosphere, OH + CH3SH → Products iii) It proceeds by two different paths, which are hydrogen abstraction reactions from the methyl group, R1, and from the sulphur atom, R2,