The thermochemical study of a purified ferrocene sample was carried out by combustion calorimetry and by differential thermal analysis. The combustion energy was determined by : - the classical method using an isoperibolic calorimeter with and without a rotating bomb from the amount of carbon dioxyde recovered after the reaction; - combustion calorimetry using about 10 mg of ferrocene and the CRMT rocking calorimeter. Comparison experiments were carried out to determine the value of the corrections to standard state. This value was also calculated directly using the energy contributions of the different constituents of the reacting system and a computer program conceived in the laboratory. Both of them are in good agreement. The values of the standard molar combustion energy resulting from this study are : -(5925 +/- 5) kJ mol(-1) (obtained by classical combustion calorimetry with a static bomb); -(5948 +/- 5) and -(5947 +/- 5) kJ mol(-1) (obtained by combustion calorimetry of small amounts of a substance and the CRMT rocking calorimeter; the first one using the comparaison experiments and the second one the computer program for calculating the value of the corrections to standard state). The second value was used to determine the following thermodynamic quantities : Delta(c)H(m) degrees(cr, 298.15 K) = -(5955 +/- 5) kJ mol(-1) Delta(f)H(m) degrees(cr, 298.15 K) = (179 +/- 5) kJ mol(-1) Delta(f)H(m) degrees(g, 298.15 K) = (253 +/- 5)kJ mol(-1) H(Fe -(c-C5H5)) = 325 kJ mol(-1) To our knowledge this study is the first one using the combustion calorimetry technique of a small amount of substance and the rocking CRMT calorimeter in the case of an organometallic compound. As mentioned in this paper, with regard to the classical combustion calorimetry which often presents great difficulties to be applied to the study of organometallic substances, this technique offers many advantages in this case.