Although many reports have already shown RSV outbreaks among hemato‐oncology patients, genomic studies detecting similar RSV strains prior to an outbreak in the hospital are rare. In 2014, the University of the Ryukyus hospital hemato‐oncology unit experienced, and successfully managed, a respiratory syncytial virus (RSV) nosocomial outbreak. During the outbreak investigation, genotyping and phylogenetic analysis was used to identify a potential source for the outbreak. Nasopharyngeal swabs were tested for RSV using three tests: (1) rapid antigen test (RAT); (2) reverse transcriptase polymerase chain reaction (PCR); or (3) quantitative PCR (RT‐qPCR); a positive PCR reaction was considered a confirmed case of RSV. Phylogenetic analysis of the G protein was performed for outbreak and reference samples from non‐outbreak periods of the same year. In total, 12 confirmed cases were identified, including 8 hemato‐oncology patients. Patient samples were collected weekly, until all confirmed RSV cases returned RSV negative test results. Median time of suspected viral shedding was 16 days (n = 5, range: 8‐37 days). Sensitivity and specificity of the RAT compared with RT‐qPCR were 30% and 91% (n = 42). Phylogenetic analysis revealed nine genetically identical strains; eight occurring during the outbreak time period and one strain was detected 1 month prior. A genetically similar RSV detected 1 month before is considered one potential source of this outbreak. As such, healthcare providers should always enforce standard precautions, especially in the hemato‐oncology unit.