The present work studied the effects of 10 mg/L cerium sulfate on the antioxidant enzymes and photosynthesis of tomato seedlings ‘Hezuo 908’ leaves under 80 mmol/L calcium nitrate stress.The results showed that,comparing with the control,calcium nitrate stress significantly inhibited the growth of tomato seedlings by reducing the height,stem diameter,fresh weight,shoot and root dry weight.Furthermore,calcium nitrate stress also led to the decreased activities of SOD,POD and CAT as well as the decreased net photosynthetic rate,stomatal conductance,transpiration rate and intercellular CO₂ concentration,whereas resulted in elevated MDA contents and membrane permeability.Comparing with the calcium nitrate stress treatments,however,after sprayed with cerium sulfate,some vegetative growth indicators,such as the plant height,stem diameter,fresh and dry weight were promoted in different degrees.In addition,the SOD,POD and CAT activities were also significantly up-regulated while MDA content and membrane permeability of leaves were greatly reduced.Meanwhile,the photosynthetic rate,transpiration rate and stomatal conductance were notably improved.Therefore,foliar spray of cerium sulfate helps to alleviate the damage caused by calcium nitrate stress through promoting the antioxidase activities,reducing the membrane lipid peroxidation and maintaining relative higher photosynthetic performance of tomato seedlings.