High temperature ceramic materials are necessary for the design of primary heat shields for future reusable space vehicles re-entering atmospheric planet at hypersonic velocity. During the re-entry phase on earth, one of the most important phenomena occurring on the heat shield is the recombination of atomic oxygen and this phenomenon is more or less catalyzed by the material of the heat shield. This paper presents some experimental results for the recombination coefficient of atomic oxygen gamma based on experiments performed on the MESOX facility using optical emission spectroscopy and actinometry techniques. Experimental results on the recombination coefficient are presented for three types of sintered ZrO2 in the temperature range 900-2500 K for 200 Pa total air pressure. These three zirconia ceramics differ essentially by the chemical nature of the sintering additives (Y2O3, CaO or MgO). A great different behavior of the recombination coefficient versus temperature is observed according to the crystalline structure of zirconia (monoclinic and tetragonal phases) and few influence of the additive is shown. (C) 2010 Elsevier B.V. All rights reserved.