Abstract: Soil acidification due to exogenous nitrogen (N) deposition has been received sufficient attention in the past several decades. Whether the N-induced soil acidification is modulated by the altering precipitation regimes remains unclear. In this study, based on a five-year (2013-2017) manipulative field experiment with factorial N addition (10 and 40 g N·m^-2·a^-1 ) and water addition (a total amount of 80 mm·a^-1 was added in terms of five intensities, i.e., 2 mm×40 times, 5 mm×16 times, 10 mm×8 times, 20 mm×4 times, and 40 mm×2 times) in a typical steppe in Inner Mongolia, I analyzed the effects of water addition on soil acidification induced by N addition. I found that soil acidification induced by 40 g N m^-2·a^-1 N addition occurred earlier, more significant, and with a greater year by year changed rate than that of 10 g N·m^-2·a^-1 N addition. After one year treatment, I observed significant soil acidification at soil profiles of 0-5, 5-10, and 10-20 cm in the treatment of 40 g N·m^-2·a^-1 N addition, while significant soil acidification in 10 g N·m^-2·a^-1 N addition was observed after 1, 4, and 5 year since N was added for the three layers, respectively. In general, the magnitude of soil acidification induced by N addition increased with the increasing period after N addition, and the slope of the regression line was steeper in the relatively higher dose of N addition (40 g N·m^-2·a^-1). Soil acidification induced by N addition could not be reversed by water addition, but water addition in terms of relatively lower intensities (i.e., all the treatments except 40 mm×2 times) could relieve the N-induced soil acidification to a certain extent in the treatment with lower dose of N addition (10 g N·m^-2·a^-1) in dry years. In wet years, however, water addition exacerbated soil acidification after N was added, especially in the topsoil. The leaching of soil inorganic N after higher intensity of water addition (10-40 mm) could explain the deteriorated N-induced soil acidification when water was added. There was no significance for the relief or deterioration to N-induced soil acidification by water addition. Our results had important implications for understanding grassland responses to N deposition and altered precipi-tation regime in the future.