Abstract: To provide a theoretical basis for rational fertilization, we explored the effects of different nitrogen (N) levels on growth, photosynthetic characteristics and saponin content of medicinal plants Panax notoginseng. Pot experiments were conducted to investigate leaf anatomy, root morphological characteristics, biomass, photosynthetic efficiency and saponin content in two-year-old P. notoginseng treated with different nitrogen levels (0 kg·hm^-2, LN; moderate nitrogen, 225 kg·hm^-2, MN; high nitrogen, 450 kg·hm^-2, HN). The results showed that the thickness of upper epidermis, lower epidermis, palisade tissue and sponge tissue reached the highest value in the HN individuals. Total root length, main root length, root surface area, number of fibrous roots, root length, root length density, root mass ratio, root shoot ratio and specific leaf area reached the maximum value in the LN individuals. Root system activity was significantly higher in the MN individuals than in the other two treatments (P<0.05). With respect to the responses of photosynthesis to light and CO₂ level, net photosynthetic assimilation, maximum photosynthetic assimilation at saturating light, carboxylation efficiency, maximum electron transfer rate and maximum carboxylation efficiency of MN individuals were significantly higher than those in the other two treatments (P<0.05). Nitrogen content per unit leaf area, chlorophyll content and the allocation of leaf N to photosynthetic tissues were highest in the HN treatment. Photosynthetic N use efficiency was the highest in the LN treatment, and total N content in roots was the highest in the MN treatment. Saponin content in roots of P. notoginseng was the lowest in the HN treatment. N surplus or N deficiency is unfavorable to growth and photosynthetic performance ofP. notoginseng. Decreased leaf thinness under LN or increased leaf thickness under HN treatment would inhibit CO₂ diffusionin leaves. Under N deficiency, more saponinlike defensive compounds are needed for the survival of P. notoginseng. Under excessive N condition, saponin biosynthesis is weakened due to lower C/N ratio.