[en] The decomposition of organic matter in soil, and the accompanying mineralization and immobilization of inorganic N, are key processes in the soil-plant N cycle. It is hypothesised that moisture regime may also play an important role on this processes of soils. Two laboratory studies were carried out to investigate the effect of moisture regime on gross mineralization, nitrification and immobilization, in a Ultisol soil, was incubated at 25^aC, under two moisture regime, field capacity (40%w/w) and 85% of field capacity (34%w/w). Using mirror image 15N isotope dilution techniques it was possible to determine that both gross nitrification and mineralization rates were greater with 85%FC, the direct nitrification rates in this soil was extremely rapid and efficient, specially with 85%FC. The immobilization and the amount of the microbial biomass N in the soil was greater with FC. The N transformations varied with moisture regime (author)