The objective of the study was to determine the prevalence and genotyping of RSV A and B in Chennai, Tamilnadu, south India. Human Respiratory Syncytial Virus (RSV) is one of the most important respiratory viruses causing acute respiratory tract infections amongst children. Based on genotyping of the attachment glycoprotein (G) gene, it is divided into two groups, RSV-A and RSV-B. We tested 850 samples from patients with influenza like illness (ILI) and severe respiratory illness (SARI) during the period 2011-2014 for RSV using a conventional RT-PCR and found 124 (14.5%) samples to be positive for RSV. Further sub typing by nested PCR in which 84(10%) were RSV A, 40 (4.5%) were RSV B, suggesting that RSV-A was the predominant group circulating in south India during the study period. Among patients with RSV infection, is 47.5% were in less than 1 year age group, 29.8 % were between 1 to 5 year age group, 14.5% were between 6 to 14 years age group and 8 % were above 14 years age. Phylogenetic analysis all RSV-A sequences belonged to ON1 within NA1 genotype and is ON1 with in NA1 genotype and RSV B sequences belonged to the genotype BA9 and BA12.