Walnut shells are a secondary biomass, with an important energy potential. In Romania nuts grow both spontaneously and in orchards. In orchards, several nuts varieties are grown, whose walnut core and walnut shells differ from one another by their chemical composition (cellulose, hemicellulose, lignin and microelements) [1-3]. In order to determine the best use of these vegetal residues we study here, comparatively, the thermal behaviour in oxidative environment and under non-isothermal conditions of the walnut shells from five nut varieties grown in Oltenia region, Romania. These nut varieties are Germisana, Jupâneşti, Lara, Valmit and Valrex. By means of a PerkinElmer DIAMOND TG/DTA thermobalance, the TG, DTG, DTA and DSC curves were simultaneously recorded at the non-isothermal linear 10 K/min heating rate of the walnut shells from these five nut varieties. After the walnut shells are devolatilised, cox burning occurs, remaining 1-2 % ash, for all of them; however, the thermal behaviour differs slightly, depending on the walnut variety. The figure is an example of calculation of the decomposition enthalpy of Lara walnut shells. In this case, oxidative decomposition occurs in several exothermic stages, the total variation of enthalpy for the decomposition is ΔH = -6484.35 J/g.