Food anticipatory activity (FAA) is an output of the food-entrained oscillator (FEO), a conspicuous biological clock which expresses when experimental animals are under a restricted food schedule (RFS). We have shown that the liver is entrained by RFS and exhibits anticipatory response prior to meal time in its oxidative and energetic state. The present study was designed to determine the mitochondrial oxidative and phosphorylating capacity in the liver of rats under RFS, to further support the biochemical anticipatory role that this organ plays during the food entrainment (Diaz-Munoz et al. 2000). Metabolic and functional parameters of liver mitochondria were characterized before (08:00 h), during (11:00 h) and after (14:00 h) FAA. The main results were: A) An enhancement during the FAA (11:00 h) in: 1) oxidative capacity (Site I of the electron transport chain), 2) phosphorylating ability (estimated by ATP synthesis), 3) activities of NADH-shuttles; B) After feeding (14:00 h), the phosphorylating capacity remained high but it was not the case for the respiratory control ratio for site I, and C) In the three experimental conditions, before, during and after the FAA, an increment was detected in mitochondrial yield and in the ⁺H-electrochemical potential (µ), the latter due to an elevation in mitochondrial membrane potential (). Most of the changes in mitochondrial properties related to RFS, were also present when comparing to a 24 h fasting group. In conclusion, the results support the notion that a distinctive rheostatic state is installed in the metabolic activity of the liver when the FEO is being expressed.