A hydroponic experiment was carried out to study effects of increased ammonium (NH₄⁺) on growth of pakchoi under light low in intensity.Results obtained show: 1) Biomass,photosynthetic rate and leaf area of pakchoi cultured in complete nitrate solution decreased by 63%,31% and 13%,respectively,in treatment 50% in light intensity and by 76%,33% and 24%,respectively,in treatment 25%,compared to those under natural light;2) Total length,surface area and volume of roots were decreased by low light intensity while average diameter was increased,but did not differ much between the three treatments different in light intensity;3) When 0.75 mmol L^-1 NH₄⁺ was added into the solution,biomass,photosynthetic rate,and leaf area of the plant peaked in treatment 50% in light intensity and increased by 90%,12% and 19%,respectively In treatment 25% in light intensity,addition of 0.50 mmol L^-1 NH₄⁺ increased the biomass,photosynthetic rate,and leaf area of pakchoi by 33%,15% and 27%,respectively;4) Root morphological parameters of pakchoi were significantly improved when a proper rate of NH₄⁺ was added,showing thatNH₄⁺ helps promote root growth.Pakchoi growth was inhibited by low light intensity through de creasing photosynthetic rate and leaf area.But addition of some NH₄⁺ into the solution could significantly offset this inhibition effect.