Independently, chronic protein malnutrition and aging have been shown to affect locomotor activity (LA) and body temperature (BT) rhythms in mammals. The objective of the present study was to ascertain the combined effects of these two factors by examining period, entrainment and other circadian parameters between LA and BT rhythms. Chronic protein malnourished (PM) and well-nourished (WN) male Sprague-Dawley rats (550-590 days of age) were implanted with activity temperature intraperitoneal radio transmitters (Mini Mitter) and exposed to different lighting protocols during at least 10 days - light-dark cycles (LD 12:12), constant darkness (DD), skeleton photoperiod (SP) and again LD. Results indicate that parametric entrainment, achieved by means of complete photoperiod, is not negatively affected in malnourished rats; however, it is affected under non-parametric entrainment like SP. A different free running period between the LA and BT circadian rhythms was detected for well-nourished and malnourished aged rats.