﻿AbstractThe Saña River Valley in Northern Peru is unusual for the western slopes of the Peruvian Andes because of its nearly year-round regime of precipitation instead of marked seasonal dry winters. This results in unexpected plant diversity. We surveyed the species ofPeperomia(Piperaceae), occurring in this valley from 300 to 3000 m elevation, based on the study of specimens from ten herbaria and field collections, resulting in a total of 81 accessions, of which 48 were made by the authors. We found 16 different taxa:Peperomiacacaophila, from Ecuador, is reported for the first time in Peru;P.cymbifolia,P.dolabriformisandP.emarginulataare reported for the first time for the Saña River Valley; other widely distributed species likeP.fraseri,P.galioides,P.haematolepis,P.hispidula,P.inaequalifolia,P.microphylla, andP.rotundatawere also found. Five species new to science are described:P.pilocarpa,P.riosaniensis, close toP.palmiformisfrom Amazonas;P.sagasteguii, related toP.trinervis,P.symmankii, close toP.ricardofernandeziifrom Piura, andP.vivipara, related toP.alata.A key to the species ofPeperomiafrom the Saña River Valley, based on vegetative characters, is provided.