In the present work, the regeneration of a spent nickel hydroxyapatite-based catalyst (Ni/Ca-HA1_S) used in dry reforming of methane (DRM) was investigated. Three successive cycles of DRM/regeneration were performed. Two different gasifying agents were tested for the regeneration step: air and carbon dioxide (21% CO2/N-2). The aim was to evaluate the ability of regeneration of the catalyst under different atmospheres. The regeneration was performed in situ at 700 degrees C under 70 mL/min of gasifying agent. Reproducible results were obtained between each cycle for the two atmospheres tested and only a small irreversible deactivation was noticed. Several characterizations (SEM, TEM, TPR, XRD) of the fresh and spent catalysts allowed proving that the irreversible deactivation was provoked by densification of nickel particles and core-shell carbon formation. Despite the slight decrease in reactants' conversions, selectivity to syngas was around 80-90% during the three cycles of DRM/regeneration with both atmospheres and no changes in the selectivity were observed. The results proved that the Ni/Ca-HA1_S catalyst could be easily regenerated under different atmospheres and make it competitive for dry reforming of methane.