Herein, we reported a so far unprecedented Mn(OAc)3·2H2O-promoted homolytic aromatic sulfonation. The reaction was performed under mild conditions with K2S2O5 employed as a green sulfonating reagent. Various arenes were successfully converted into desired sulfonic acids or sulfonates in high efficiency. Preliminary mechanistic studies demonstrated that the present reaction proceeds via a homolytic aromatic substitution-type mechanism involving an SO3- radical. The combination of Mn(OAc)3·2H2O and HFIP plays a crucial role.