To evaluate clinical effect and immunological mechanism of intravene ous immunoglobulin (IVIG) for the treatment of bronchiolitis induced by respirat ory syncytial virus (RSV) in infants, the levels of serum interleukin 6 (IL- 6), interleukin 8 (IL-8) and tumor necrosis factor-α (TNF -α) were determined before and after IVIG therapy in 26 cases with IVIG therapy, 30 cases with the conventional therapy and 40 cases as normal controls , respectively. The recovery time of the clinical signs and symptoms and duratio n of hospitalization were also compared between the IVIG group and the conventio nal group. The results showed that the levels of IL-6, IL-8 and TNF-α were significantly higher in two groups before treatment comparin g to normal infants. These cytokines tended to decrease after IVIG therapy altho ugh no significantly difference was observed between the IVIG group and the conv entional group. It was noticed that the recovery time of clinical wheezing and l ung signs were obviously shortened in the IVIG group comparing to the convention a l group (4.0±2.1 Vs. 5.2±1.4days; 5.4±1.5 Vs. 6.5±1.8days, P ＜0.001， P＜0.05). No significantly difference of hospitalization days w as observed between two groups (9±2.2 Vs. 10.3±3.1days, P＞ 0.05). It is concluded that cytokines involves in the pathogenesis of bronchiolitis ind uced by RSV in infants, and IVIG therapy can be helpful for the improvement of t he clinical situation. However, the inhibitory effect on the production of cytok ines seems not to be obvious when single　IVIG　therapy　is given at a dose of 0.25g/kg.