This experiment was conducted to evaluate the effects of coated acidifier, small peptide chelate iron and their interaction on performance, the contents of trace elements in egg yolk and immune and antioxidant indices in serum of laying hens in egg laying peak in summer. Five hundred and seventy-six healthy Roman pink-shell laying hens at 38-week-old were randomly allotted to eight groups with six replicates per group and twelve hens per replicate according a 2×4 factorial completely randomized design with two supplemental levels of coated acidifier and four supplemental levels of small peptide chelate iron in the basal diets. The hens in groups A, B, C and D were fed the basal diet supplemented with 0 mg/kg coated acidifier and 0 (control group), 0.04%, 0.08% and 0.12% small peptide chelate iron (the content of Fe was 0, 60, 120 and 180 mg/kg, respectively), and those in groups E, F, G and H were fed the basal diet supplemented with 300 mg/kg coated acidifier and 0, 0.04%, 0.08% and 0.12% small peptide chelate iron (the content of Fe was 0, 60, 120 and 180 mg/kg, respectively). The pre-test lasted for one week, and the experiment lasted for six weeks. The results showed as follows:1) coated acidifier, small peptide chelate iron and their interaction had no significant effects on average daily feed intake (ADFI), laying rate and the ratio of feed to egg of laying hens at the 3rd and 6th weeks (P>0.05). ADFI in group G was significantly higher than that in the control group and groups C and D at the 3rd and 6th weeks (P<0.05), laying rate in group B was significantly higher than that in the control group and groups D and E at the 6th week (P<0.05), and the ratio of feed to egg in group B was significantly lower than that in group D at the 6th week (P<0.05). Coated acidifier had significant effects on egg weight at end of the 3rd week and egg yolk index and Haugh unit at end of the 6th week of laying hens (P<0.05), small peptide chelated iron had significant effect on egg yolk index at the end of the 6th week (P<0.05), and their interaction had significant effects on the egg yolk index (P<0.01) and Haugh unit (P<0.05) at end of the 6th week. At end of the 3rd week, egg weight in group G was significantly higher than that in group B (P<0.05), and egg yolk index in groups G and H was significantly higher than that in group C (P<0.05). At end of the 6th week, egg weight in groups C, D and G was significantly higher than that in the control group (P<0.05), egg yolk index in group F was significantly higher than that in groups C, D and E (P<0.05), and Haugh unit in groups E, F and G was significantly higher than that in group D (P<0.05). 2) Small peptide chelated iron and the interaction of coated acidifier and small peptide chelated iron had significant effect on the content of iron in egg yolk of laying hens at end of the 3rd and 6th weeks (P<0.01). The content of iron in egg yolk in groups B, C, D, F, G and H was significantly higher than that in the control group and group E at end of the 3rd and 6th weeks (P<0.01), the content of iron in egg yolk in group H was significantly higher than that in groups B and F (P<0.05) and the content of zinc in egg yolk in group H was significantly higher than that in group F (P<0.05) at end of the 3rd week, and the content of zinc in egg yolk in group B was significantly higher than that in group D at end of the 6th week (P<0.05). 3) Coated acidifier had significant effects on the activity of total superoxide dismutase (T-SOD) (P<0.01) and the content of malondialdehyde (MDA) (P<0.05) in serum of laying hens, and the interaction of coated acidifier and small peptide chelated iron had significant effects on the activity of T-SOD in serum (P<0.01). The content of immunoglobulin M (IgM) in serum in group C was significantly higher than that in the control group (P<0.05), the activity of T-SOD in serum in groups D, E, F, G and H was significantly higher than that in the control group (P<0.01), and the content of MDA in serum in groups B, F and G was significantly lower than that in the control group and group E (P<0.05). In conclusion, dietary 0.04% and 0.08% small peptide chelated iron alone or combined with 300 mg/kg coated acidifier is benefit to maintaining and extending the egg laying peak of laying hens in summer, improving egg quality, enrichment of iron in egg and enhancing antioxidant capacity.