This article investigates rationalistic sectarian movements of a Protestant nature that gained prominence within the territory of Tobolsk province from the late nineteenth century through the early twentieth century. The study draws upon archival documents housed at the State Archive of Tobolsk as well as publications in the local ecclesiastical newspaper “Tobolskiye Eparkhialnyye Vedomosti” and works authored by representatives of Orthodox clergy. Analysis of these sources leads to several key conclusions. Firstly, it is observed that Protestant sects such as Stundists, Baptists, Mennonites, and Adventists began appearing on provincial soil towards the end of the nineteenth century. Secondly, the growth in numbers of adherents to these sects was significantly influenced by legislation enacted between 1905 and 1906 which introduced greater religious tolerance. Furthermore, the dissemination of foreign-derived rationalist doctrines emerged as an important trend in the evolution of Russian religious sectarianism during this period. A critical finding is highlighted regarding challenges faced by both provincial and diocesan authorities when attempting to categorize specific religious communities into distinct rationalist sectarian categories. These difficulties stemmed not only from the sheer diversity of theological interpretations but also from common practices among Stundists, Baptists, and Mennonites who frequently shifted allegiances across different denominations. Lastly, while new teachings rarely held broad appeal for indigenous Siberian populations, increases in sect membership were largely driven by migration patterns involving settlers relocating from European and southern regions of Russia.