Sanchezia dubia is described and illustrated as a new species from the department of Madre de Dios in southeastern Peru. Its morphology slightly resembles Sanchezia sprucei, but its most remarkable feature is its close similarity to Suessenguthia, even more so than to those of its own genus. This new species is distinguished from others by its glabrous stem and leaves, its inflorescence containing two to five serial cymose heads, which are sessile to short-pedunculate, with mostly two to four flowers each (occasionally one), its inner bracts ranging in length between 6 and 23 mm, and its androecium composed of two stamens and two mucronate staminodes. We suggest it is an endangered species based on its restricted geographic distribution, its few known populations, and the increasing threats to its habitats. Along with Suessenguthia koessleri, this new species seems to be a key taxon to understanding the phylogenetic relationship between these two genera, which is still uncertain. Additionally, we provide a key to identify the Sanchezia and Suessenguthia species of the Madre de Dios River basin from southern Peru to northern Bolivia.