The Selective Catalytic Reduction of NOx by ammonia (NH3-SCR of NOx) was studied over an iron Colombian natural zeolite (Nat-zeo) based geo-catalysts after several treatments (H-zeo-Fe3+ and H-zeo-Fe2+) under lean, dry and wet conditions. Nat-zeo from the Combia geological formation in Colombia (South America) was treated with NH4NO3, calcined in air for obtaining H-zeo-Fe3+ and then reduced with hydrogen to obtain the H-zeo-Fe2+ catalyst. Catalysts were characterized by XRD, FTIR, Mossbauer spectroscopy, SEM/EDX, XRF BET, H-2-TPR, NH3-TPD, and NOx-TPD. H-zeo-Fe3+ showed better catalytic performance than Nat-zeo and H-zeo-Fe2+ in the NOx conversion. The presence of Fe3+ ions and the acidity in the catalyst explains partially the high activity towards NOx reduction. Water inhibits the NO and improves the NO2 adsorption on the catalyst H-zeo-Fe3+ surface according with the NOx-TPD analysis. After 30 h on-stream, under wet conditions, the H-zeo-Fe3+ catalyst showed a decreased in the NOx conversion. The decrease of activity could be related with the loss of catalyst surface acidity detected by NH3-TPD analysis after reaction and with the contraction of the zeolite channels due to the metaheulandite phase formation that was confirmed by XRD, BET and FTIR analysis.