5-aminolevulinic acid (5-ala) was used for detecting cancer, recently studies showed the antioxidant effect in 5-ala that enhanced heme oxygenase-1 (HO-1). HO-1 is produce carbon monoxide, biliverdin and iron. The iron is recycled by the cells and is essential for the production of red blood cell (RBC). Iron deficiency anemia is recognized as a serious disorder in many livestock animals, especially piglets. Anemia characterized by a low hemoglobin (Hb) concentration (HbC) is common in indoor-housed pregnant sows. In this study, we investigated the effect of 5-ala supplementation on growth, performance, and hematological changes in weaned pigs. A sow herd with biweekly batch farrowing was selected for the study, and 100 sows at mid-gestation were randomly assigned to either a treatment or control group. We found that 5-ala significantly increased Hb values including the HCT and HbC in sows. Unlike the RBC count, the white blood cell count, particularly the neutrophil count, was decreased in sows. In addition, hydrogen peroxide, an oxidative stress marker, was increased in the sows’ saliva. Furthermore, the 5-ala treatment significantly enhanced body weight gain in both the suckling and weaning piglets groups. However, the RBC count showed a tendency to increase, but there was no c...