Microlinus Casey, 1906 is a monotypic genus known only from the USA, Jamaica, Trinidad and Tobago, and Ecuador (Galápagos). Recently, one new species was found in southern Brazil, and it is here described and illustrated. Microlinus perobanus Busanello and Caron, new species, differs from Microlinus pusio (LeConte) by having the head and abdomen darker than the rest of the body, the labrum truncate on anterior margin, and the apex of the median lobe of the aedeagus clearly tapered and pointed. A key to the species of Microlinus is provided. The new Brazilian record extends the distribution of the genus into the southern portion of South America.