There is a risk of iron overload in grazing livestock. However, the effects on nutrient absorption and rumen function induced by excessive iron have not been well understood. Therefore, the purpose of present study was to investigate the impact of over-load iron on growth performance, nutrient digestibility, blood biochemistry, rumen fermentation and bacterial communities in sheep. Twenty-four German Mutton Merino cross-bred sheep with weight (42.66 ± 2.34 kg BW) were randomly divided into 4 groups, each with 6 replicates and 1 sheep per replicate. The basal diet consisted of 60% Leymus chinensis hay and 40% concentrate. The sheep in 4 groups were fed the basal diets supplemented with 50 (Control), 500 (T1), 1,000 (T2) and 1,500 (T3) mg Fe/kg as ferrous sulphate monohydrate (FeSO 4 ·H 2 O) respectively.And the actual contents of iron in the diet were determined to be 457.68 (control), 816.42 (T1), 1,256.78 (T2) and 1,725.63 (T3) mg/kg respectively. The experiment lasted 62 days including a 7-day metabolism trial. During the whole experiment, the digestibility of dry matter, organic matter, neutral detergent fibre and acid detergent fibre showed a quadratic increase with increasing over-load iron levels (p < .05), and