This experiment was conducted to evaluate the effects of coated acidifier and small peptide chelated iron and their interaction on laying performance, egg quality and serum biochemical parameters of 38- to 44-week-old laying hens in summer. A 2×4 factorial completely randomized design was adopted with 2 supplemental levels (0 and 300 mg/kg)of coated acidifier and 4 supplemental levels (0, 0.04%, 0.08% and 0.12%)of small peptide chelated iron in the basal diet. A total of 576 healthy Lohmann pink-shell laying hens (38-week-old) were randomly allotted to 8 groups with 6 replicates of 12 hens per replicate. 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% or 0.12% small peptide chelated iron (the content of iron 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% or 0.12% small peptide chelated iron (the content of iron was 0, 60, 120 and 180 mg/kg, respectively). The adjustment period lasted for 1 week, and the experimental period lasted for 6 weeks. The results showed as follows:1) coated acidifier and the interaction of coated acidifier and small peptide chelated iron had a significant effect on Haugh unit (P<0.05). Total egg number in groups B and H was increased by 4.57% and 4.45%, respectively, compared with control group (P>0.05). Egg shell thickness in group F was significantly higher than that in control group (P<0.05). Feed to egg ratio in groups B and H was significantly higher than that in group G (P<0.05). Haugh unit in groups E, F and G was significantly higher than that in group D (P<0.05). 2) Coated acidifier had no significant effects on serum biochemical parameters (P>0.05). Small peptide chelated iron had significant effects on serum calcium, phosphorus and iron contents (P<0.05). The combination of coated acidifier and small peptide chelated iron had significant effects on serum total cholesterol, calcium and phosphorus contents (P<0.05). Serum alkaline phosphatase activity in group D was significantly lower than that in control group (P<0.05). Serum total cholesterol content in group H was significantly lower than that in groups B and C (P<0.05), and was decreased by 15.48% compared with control group (P>0.05). Serum calcium content in groups B and F was significantly higher than that in group E (P<0.05). Serum phosphorus content in group C was significantly higher than that in group E (P<0.05). Serum iron content in group C was significantly higher than that in control group and groups E and H (P<0.05). In conclusion, adding 0.04% small peptide chelated iron alone or combined with 300 mg/kg coated acidifier are beneficial to improve the laying performance, egg quality and serum biochemical parameters of 38- to 44-week-old laying hens in summer.