ABSTRACT: The preventive effects of ACTICOA powder (AP), a cocoa polyphenolic extract, on free radicals produced by leucocytes in rats after heat exposure (HE) and its protective effects on subsequent cognitive impairments were assessed. AP or vitamin E, the antioxidant reference, was orally administered to rats for 14 d before HE at 40 °C temperature during 2 h. The day after HE, free radical production by leucocytes in rats treated with AP or vitamin E was significantly reduced as compared to control. Unlike controls, AP- and vitamin E-treated rats discriminated between active lever and inactive levers in a light extinction paradigm. In the Morris water maze, escape latencies before reaching the hidden platform by AP- and vitamin E-treated rats decreased throughout testing. The daily oral administration of AP or vitamin E protected rats from cognitive impairments after HE by counteracting the overproduction of free radicals.