Abstract: Oilseed flax is an important oil crop in northern China. Field experiments were carried out to study the effects of nitrogen application rate on yield, quality and nitrogen use efficiency with an aim to provide guideline of oilseed flax fertilization. Compared to no N application, 90 kg·hm^-2 N treatment increased yield of 27.35%, increased pod per plant, seeds per pod, yield per plant and protein content by 23.1%, 7.47%, 48.9% and 14.0%, respectively. Though 90 kg·hm^-2 N treatment decreased the days from emergence to anthesis, seed filling period and apparent recovery efficiency were increased. 1000-seed weight and seed oil content were not affected by N fertilizer. In conclusion, the present study indicates that N fertilizer promotes the growth of oilseed flax and development, increasing nitrogen uptake rate, to improve protein content, but physiological efficiency of nitrogen decreased significantly. Based on oilseed flax yield and N use efficiency, the optimum N fertilizer application rate was 90 kg·hm^-2.