The purpose of this study is to determine the growth performance and immune characteristics of early weaned piglets receiving rice bran expressing porcine lactoferrin as a feed additive. Full-length cDNA encoding porcine lactoferrin (LF) driven by a rice actin promoter was transformed into rice plants, and its integration into the rice genome was verified by Southern blot analysis. The expression of recombinant LF (rLF) in whole grains and rice bran was also confirmed, and the amount of rLF accumulated in rice bran was estimated by immunoblot assay to be approximately 0.1% of rice bran weight. An iron-binding assay showed that the rLF retained iron-binding activity and the binding capacity of 1 mg/mL rLF would be saturated by 100 microM of FeCl(3). Thirty-six early weaned piglets at 21 days old were randomly selected into two groups and fed a diet containing 5% transgenic rice bran containing 50 mg/kg rLF (rLF group) and 5% rice bran (control group) to investigate the piglets' growth performance and immune characteristics. The results showed no significant difference in growth performance between the groups during the feeding period. However, the aerobic bacteria, anaerobic bacteria, and coliform counts in the cecal contents of the rLF-fed group were significantly lower than those of the control group. Additional immune characteristics such as the IgG concentration in the rLF group was higher than the control group at the 28th day, but leukocyte counts and the peripheral lymphocyte ratio remained similar. In summary, porcine LF expressed in rice bran, a byproduct of rice, can be used as a functional additive to improve antimicrobial capabilities and IgG concentration of early weaned piglets.