The locality of Sant Jaume de Frontanyà (Eastern Pyrenees, Catalonia, northeastern Spain) includes four fossil-bearing levels with an extraordinary abundance of mammal remains, representing the most significant middle Eocene site from the Iberian Peninsula. Despite this, the fauna from this locality has not been studied in detail. Recent work has mostly focused on the primates from the oldest levels, including the description of two new species, Anchomomys frontanyensis and Pseudoloris pyrenaicus. Recently, study of the primate remains from the uppermost level, Sant Jaume de Frontanyà-1 (SJF-1), has led to the description of a new species of Necrolemur. On the other hand, other mammal groups such as rodents are practically undescribed. In this work, rodent remains from SJF-1 are described for the first time. Three different forms have been identified: one glirid, referred to Glamys aff. robiacensis, and two theridomyids that have allowed the erection of the new species Paradelomys santjaumensis and Elfomys catalaunicus, suggested to be the most primitive members of the genera Paradelomys and Elfomys. These three forms show more primitive traits than other species from upper Bartonian (MP16) localities such as Robiac, Grisolles, and Le Bretou. Locality SJF-1 is therefore assigned to the lower Bartonian (MP15), with an age slightly older than Chéry-Chartreuve, and represents the first occurrence of the genera Paradelomys and Elfomys. Moreover, this dating allows us to place the only record of Necrolemur from the Iberian Peninsula in a correct chronological framework, shedding new light on the evolution of this primate genus.