Metal chalcogenides with various channel structures feature a number of interesting properties including fast-ion conductivity and selective ion exchange. Most of these compounds are popularly prepared based on the templates of organic amines that play the part of a structure directing agent and even structure-building units, while it still remains a challenge as to the organotemplate-free synthesis for these compounds. Here, a new ternary thiostannate (H3O)4Cu8Sn3S12 was synthesized through a facile, efficient, and organotemplate-free route under hydrothermal conditions. The framework of (H3O)4Cu8Sn3S12 consists of [Cu8Sn6S24]8- building units and possesses a 3D interconnected 8-ring channel structure decorated by pure hydroniums, which not only balance the charges but also facilitate the proton conductivity. The proton conductivity reaches as high as 1.03 × 10-3 S cm-1 at 393 K under anhydrous conditions, which is 2 orders of magnitude higher than that of (H3O)2(enH2)Cu8Sn3S12, a similar channel structure compound prepared by using ethylenediamine as an organic template.