Objective To analyze respiratory syncytial virus infection in infants and young children during 2014 and explore the relationship of infection status with the level of interleukin-4 in serum samples.Methods Totally 150 children with ARI were recruited in this study,and collected throat swabs from them.RSV was identified and differentiated into subgroups A and B by real-time RT-PCR.The total of IL-4 concentration in serum samples was measured by ELISA.Results Out of the 150 samples,32 (21.33％) were positive for RSV.Subtyping for A and B showed that 25 cases were subgroup A and 7 cases were subgroup B.Comparing between RSV infection group and normal control group,the former had higher serum IL-4 level [(328.67 ± 52.96) ng/L vs.(217.34 ± 51.21) ng/L,P ＜ 0.01],additionally B subgroup presented higher concentration than A subgroup [(371.09 ± 61.96)ng/L vs.(316.80 ± 44.63) ng/L,P ＜ 0.05].Analysis of clinical data indicated that infection of B subgroup probable caused more serious wheeze symptoms than that by subgroup A.Conclusions Infection of RSV subtype A was predominant in Oct.2014 to Mar.2015.Level of serum IL-4 was increased statistical significantly after RSV infection.Furthermore,infection of subtype B might cause more severe illness.