A new species of Hypsiboas is described from the Atlantic Forest in Santa Catarina State, southern Brazil. The new species is morphologically similar to Hypsiboas marginatus, from which it differs by its smaller size, flanks with white blotches, a white stripe on the upper lip exceeding posteriorly to the tympanum, a white dorsolateral stripe reaching the inguinal region, tadpole with body black, tail whitish-yellow translucent, and labial tooth row formula 2(2)/5(1). The new species inhabits Atlantic Forest environments within mountain ranges from eastern Santa Catarina State, denominate Serras do Leste Catarinense, while H. marginatus occurs in the Serra Geral mountain range, in southern Santa Catarina and northeast Rio Grande do Sul State, and thus have allopatric distributions. The new species is included in the Hypsiboas pulchellus species group, and its relationship with other members of the group is discussed herein. We also discuss the conservation status of the new species in relation to the IUCN Red List Categories and Criteria of threatened species.