BACKGROUND Nosocomial infections are a major cause of death in premature infants, especially in very low birthweight (VLBW) infants. The VLBW infants have low serum immunoglobulin G levels, which may have an effect on infections in early infancy. Thus, prophylactic administration of intravenous immunoglobulin (IVIG) is proposed to maintain higher immunoglobulin G and reduce the rate of hospital-acquired infection. METHODS A study for the effects of prophylactic IVIG therapy in VLBW infants was performed. A total of 61 VLBW infants were enrolled, and divided into the IVIG group (n = 31) and the control group (n = 30). The dose for each infant was 750-1000 mg/kg for those whose birthweight was less than 1000 g, and 500-750 mg/kg for infants whose birthweight was between 1001 and 1500 g. The control group received saline infusion. The infusions were given every 2 weeks until the infant weighed 1800 g, or was discharged. RESULTS The results showed: there were no major differences in the perinatal and neonatal characteristics between the two groups, consistently higher IgG levels were found in the IVIG group, and the age of first documented sepsis was earlier in the control group. CONCLUSIONS In this study, the prophylactic IVIG therapy may give substantially higher IgG levels, which may last for 2 months. However, a prophylactic effect for hospital-acquired infections was not observed.