In recent years, methylated thioarsenicals have been widely detected in various biological and environmental matrices, suggesting their broad involvement and biological implications in arsenic metabolism. However, very little is known about the formation mechanisms of methylated thioarsenicals and the relation between arsenic methylation and thiolation processes. It is timely and necessary to summarize and synthesize the reported information on thiolated arsenicals for an improved understanding of arsenic thiolation. To this end, we examined the proposed formation pathways of methylated oxoarsenicals and thioarsenicals from a chemical perspective, and proposed a new arsenic metabolic scheme in which arsenic thiolation is integrated with methylation processes (instead of being separated from methylation as currently reported), followed lastly by discussion on the biological implications of the new scheme of arsenic metabolism. This informative review on arsenic thiolation from the chemical perspective will be helpful to better understand the arsenic metabolism at the molecular level and the toxicological effects of arsenic species.