This study evaluated the validity of Bergmann’s and Allen’s ecogeographic rules in two coexisting sigmodontine rodents, Abrothrix olivacea and Phyllotis darwini, along an elevational gradient in central Chile. Morphological measurements of body, cranial, and appendage size were analyzed across altitudes from 154 to 2560 meters. Weak support was found for both rules. While A. olivacea showed increased cranial size with elevation (supporting Bergmann’s rule), P. darwini showed a reverse pattern. Allen’s rule was supported only by ear length in both species. These findings suggest species-specific responses to thermal gradients and highlight the role of behavioral and ecological adaptations over strict morphological change.