A field experiment was conducted to determine the effect of doses N on yield and quality of chose in Gialam, Hanoi. Five nitrogen rates were compared to 0: 30; 60; 120; and 180 kg N/ha. The highest yield (fresh matter and dry matter) of choysum was obtained at 120 kg N/ha in both summer and winter season. Application over 120 kg N/ha, is at 180 kg N/ha was not significantly increase yield. Nitrat content increased according with N applied rates from 0 to 180 kg N/ha. Nitrat content for a given nitrogen application was higher in winter season than in summer season. A tentative critical N dilution curve has been set up for choysum crop; this curve is described by the following equation: Nc = 4,934 x DM-0.054 (R2 = 0,707). This curve has been validated over the range of shoot dry matter of 0,12-2,18 t/ha. For lower shoot biomass, this equation overestimated the critical nitrogen concentration. The validity of this curve needs to continue evaluating in different climates and cultivation conditions.