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[Objectives] The research was aimed to study the effect of a nano-iron oxide(ferrihydrite) on maize growth and antioxidant system and to provide theory basis for ferrihydrite used as a new iron fertilizer on maize growth. [Methods] Deionized water(CK1) was set up as control while a series of ferrihydrite, i.e. 10, 20, 50, 100, 200 and 500 mg·L-1 were used as treatments during seed germination. Then seedlings were transferred to 1/2 Hoagland solution without iron(CK2) and with EDTA chelated iron(CK3) while a series of ferrihydrite, i.e. 10, 20, 50, 100, 200 and 500 mg·L-1 with CK2 solution were used as treatments. The biological and physiological indicators as well as cell micro-morphological structures were determined during maize seed germination and seedling growth. [Results] The seed germination experiment results showed that the germination index, the vigor index and the average root length increased significantly by 38.33%, 61.99% and 53.91%, respectively, and the average germination time reduced by 56.63%, when the concentration of ferrihydrite was 20 mg·L-1 as compared with CK1. The seedling growth experiment results showed that the fresh weight of shoot, root of length and chlorophyll content increased significantly by 15.38%, 10.03% and 24.85% as compared with the CK2, when the concentration of ferrihydrite was 20 mg·L-1. Concentration higher than 50 mg·L-1 had damaged maize growth. Ferrihydrite concentrations of less than 20 mg·L-1 increased POD and CAT activities in maize leaves. However, the concentrations of more than 20 mg·L-1 led to the gradual reduction of POD and CAT activities. In addition, results of leaf Fe determination and transmission electron microscopy observation showed that ferrihydrite at the concentration of 10 mg·L-1 could enter the root cells of maize and significantly increased the content of iron in shoot by 75% as compared with CK2. However, higher ferrihydrite concentration of more than 20 mg·L-1 resulted in the plasmolysis of root cell. [Conclusions] The promoting effect of ferrihydrite on seed germination and growth of maize seedlings suggested that low lever ferrihydrite(10-20 mg·L-1) could be used as an alternative for EDTA-Fe, whereas high concentrations of ferrihydrite(≥ 50 mg·L-1) damaged maize growth [ABSTRACT FROM AUTHOR]