Abstract: The chloride(Cl) ion is present in abundance almost everywhere in the world.It is required as a micronutrient for optimal plant growth.The influence of the chloride ion on plant growth depends on the plant variety.The dependence of modern agriculture on irrigation and chemical fertilization causes more concern about chloride toxicity than deficiency.The impact of Cl ion might help to increase N use efficiency in many crop plants.However,the studies mentioned above provided little information on sunflower(Helianthus annuus).There are great differences in tolerance to chloride salts among crops.So far,studies on chloride tolerance of sunflower have been very limited.Seedling growth rate,dry matter accumulation rate per plant,Cl-,NO3-,N,P and K content in sunflower seedlings under different chloride concentration treatments were studied in hydroponic experiment.The results showed that stem growth rate decreased significantly under Cl-6.25-25 mmol/L for 8 d,the higher the concentration of Cl-,the greater the decrease of plant growth.Dry matter accumulation rate of Cl-6.25-25 mmol/L treated seedlings were more than that of control,while no significant difference was found among dry matter accumulation rate of Cl-25,50 mmol/L treated seedlings and control seedlings.Dry matter accumulation of Cl-200300 mmol/L treated seedlings was obviously less than that of control.Chloride content in plant was significantly increased,while nitrate content decreased under chloride treatments.Nitrate content of Cl-50 mmol/L treated seedlings was the lowest among those treatments.N,P content of stem and leaf in Cl-6.25-100 mmol/L treated seedlings did not differ significantly from control.N content of stem and leaf in Cl-200 mmol/L treated seedlings decreased obviously,while the N and P content in root increased with supplemental Cl-concentration.K content in root,stem and leaf of seedlings gradually increased with supplemental Cl-concentration.Thus,nitrogen utilization efficiency of sunflower seedlings was increased while biomass accumulation of plant was not affected or increased under supplemental Cl-treatments(Cl-6.25-50 mmol/L).However,growth of sunflower seedlings was inhibited when being exposed to high level supplemental Cl-(Cl->100 mmol/L) due to reduced nutrient absorption.