Four letters of the founder of an Irkutsk historical dekabristovedeniye Boris Georgiyevich Kubalov to the famous Siberian historian to professor to the YOKE to Fedor Aleksandrovich Kudryavtsev written in 1957–1963 and found by the author in GAIO funds are published in the present article. Letters help the researcher to study the last years of life of Kubalov in Moscow, in detail to define a circle of his scientific interests and plans. These documents open as well «inner world» of the scientist, confirm big love of the teacher to the pupil, to Irkutsk and inhabitants of Irkutsk, to Siberia and the Siberian history.