Abstract: The effects of iron deficiency and NO₃^- stress on the growth and the iron absorption cha-racteristic of tomato seedlings were investigated under suboptimal temperature (18 ℃/12 ℃ (day/night)). The results indicated that the growth was significantly inhibited under suboptimal temperature compared with appropriate temperature treatment; the plant heights, leaf areas and dry matter accumulations were markedly decreased. The effects of iron deficiency under suboptimal temperature on the growth of tomato seedlings were larger than that of under appropriate temperature treatments. Under suboptimal temperature, the plant heights of tomato seedlings in iron deficiency and/or NO₃^- stress treatments were not significantly different from no stress treatment, but leaf areas and leaf chlorophyll content of tomato seedlings were decreased obviously. The leaf electrolytic leakage, root activity and Fe³⁺ reductase activity of tomato seedlings were markedly increased under suboptimal temperature, but chlorophyll content, total root length, root surface area, root tip number and root volume were obviously reduced. The iron contents in roots, stems and leaves of tomato seedlings were also remarkably decreased. The NO₃^- stress and the combined stress of iron deficiency and NO₃^- stress under suboptimal temperature aggravated the reduction of dry matter, leaf electrolytic leakage and the inhibition of iron ion absorption in tomato seedlings. The iron ion absorption showed the antagonistic impact on the absorption of potassium and calcium ion, but showed different effects among different organs. The iron deficiency symptom of tomato seedlings was aggravated by reducing the concentration of iron ion in the nutrient solution.