Forest plantings of Pinus radiata are a form of disturbance that may affect wildlife populations. The majority of these exotic forests are concentrated in an area of central Chile (VIII Region) in which the natural history and ecology of small mammals is poorly known. Population characteristics of a small mammal assemblage inhabiting the shrubby under-story of P. radiata forests were studied. These data were then compared with information documented for less disturbed habitat types of central and southern Chile. Seven species of small mammals were captured during an 18 month census utilizing Sherman live-traps. These species were the cricetid rodents Abrothrix olivaceus, Abrothrix longipilis, Phyllotis darwini and Oryzomys longicaudatus, the octodontid rodent Octodon bridgesi, the murid rodent Rattus norvegicus, and the didelphid marsupial Marmosa elegans. The two Abrothrix species were the most abundant, with densities greater than those documented for central Chile. The reproductive periods were more similar to those known for populations of the semiarid and mediterranean scrub of northern and central Chile, than to those of temperate rainforests in southern Chile. Monthly population fluctuations of some species coincided in some cases with patterns documented in northern and southern Chile. Two species showed a maximum and minimum home range during spring and winter, respectively; whereas two other species had a maximum and minimum home range during summer and fall, respectively. The remaining species did not show any cler-cut pattern. Small mammal activity periods were similar to those reported in central Chile.