A morphological study of small body sized Mannophryne frog specimens from the Sierra de San Luis, Venezuela, revealed that they belong to an undescribed species. By having a narrow collar, the new species differentiates from all Mannophryne having a wide collar (a character present in almost half of the species included in this genus). From the rest of narrow-collared Mannophryne it is easily differentiated by a combination of different foot-web formula and pattern of coloration. The geographically closest species is M. caquetio Mijares-Urrutia & Arends, 1999, from which it differs by having a distinctive pattern of coloration, different shape of the tip of the snout, size of tympanum, degree of detachment of tongue from floor of mouth, by having lateral fringes along toes not forming flap folding on digits, and by having a more extensive foot-web.The most closely resembling frog to the new species is M. lamarcai Mijares-Urrutia & Arends, 1999, from which it differs by having a distinctive pattern of coloration, of which it stands out the uniformly dark dorsum without dorsolateral bands; also, by having the tip-of-snout truncated, lateral flaps along toes not folding onto digits, and less foot-webbing. The new species comes from a Premontane humid forest that is completely isolated by surrounding dry forests and raises to three the known members of the genus in Falcon State, a Venezuelan geopolitical division still lacking complete herpetological inventories. It is the northernmost Venezuelan and continental South American Mannophryne, rising to 21 the known species in the genus. In this paper we describe the new species, provide a diagnosis comparing it to all known members ofthe genus, and provide data on its biogeography, ecology, and conservation.