Trichomycterus lauzannii, new species, is described from the upper Río Beni basin in La Paz, Bolivia. The new species is distinguished from congeners by the posterior cranial fontanel reduced to a small round opening on the posterior portion of supraoccipital bone and the possession of a rounded anterior cranial fontanel between frontal bones. In addition, the new species can be further distinguished from congeners by the possession of seven or fewer odontodes in the opercular patch, a pelvic fin which does not reach the anus when depressed, round blotches along the side of body, a first pectoral-fin ray prolonged as a short distal filament, and several meristic and morphometric features. Comparisons are given with similar congeners (T. cachiraensis, T. megantoni, T. sketi, and T. steindachneri).