Abstract: Objectives The aim of this study was to investigate the effects of enhanced ammonium (NH4+) on the growth and nitrogenous metabolisms of cotton grown hydroponically under low-temperature stress.Methods Using cotton (Gossypium hirsutum L. cv. Xinluzao13) as the experimental material, we studied the influences of the different ammoniam/nitrate ratios (NH4+-N/NO3--N of 0/100, 25/75, 50/50, 75/25, 100/0) on the growth, nitrogen uptake and accumulation, NO3- concentration, and the activities of nitrate reductase (NR), glutamine synthetase (GS) and glutamine 2-oxyoglutarate aminotransferase (GOGAT) activity in cotton seedlings grown in a growth chamber under low-temperature stress (15℃). Results The combined supply of ammoniam with nitrate significantly enhanced (P 0.05) the biomass of different organs of cotton grown under the normal condition (25℃). The dry matter yields of both shoots and roots were the biggest at the ammoniam/nitrate ratio of 50/50 and the smallest at the ammoniam/nitrate ratio of 100/0. The biomass of different organs of cotton was significantly decreased under low temperature (15℃). Nitrogen concentrations and the activities of GS and GOGAT increased with increasing of NH4+/NO3- ratios, but nitrogen accumulation increased firstly and then decreased in cotton seedlings grown under either normal or low temperature. The nitrate concentration in different organs of cotton seedlings, together with NR activity of cotton leaves decreased under either normal or low temperature. Nitrogen accumulation of cotton seedlings, nitrate concentration, and NR, GS and GOGAT activities decreased significantly under low-temperature stress.Conclusions The combined supply of ammoniam with nitrate could enhance the concentration of nitrogen and NO3--N, and the activities of GS and GOGAT of cotton seedlings, thus maintaining the balance of nitrogenous metabolism and enhancing the plant resistance to low-temperature stress, and the growth and biomass of cotton seedlings.