The writer's letters are important material for studying his biography and his works; they unveil the cultural-historical context of the literary works creation and can be essential to define the author's intention, conception and strategy. The following work offers classification and general characteristic of theMamin-Sibiryak' sepistolary heritage. We registered the writer's epistolary circle and its main groups that include members of the family, friends, literature magazines' editors etc. We also identified the publishing background of Mamin-Sibiryak's letters and outlined the amount of letters that have not been published before.