For molecular study of marine bacteria Pseudoalteromonas phenolica using bacteriophage, a novel bacteriophage, TW1, belonging to the family Siphoviridae, was isolated, and its genome was completely sequenced and analyzed. The phage TW1 genome consists of 39,940-bp-length double-stranded DNA with a GC content of 40.19 %, and it was predicted to have 62 open reading frames (ORFs), which were classified into functional groups, including phage structure, packaging, DNA metabolism, regulation, and additional function. The phage life style prediction using PHACTS showed that it may be a temperate phage. However, genes related to lysogeny and host lysis were not detected in the phage TW1 genome, indicating that annotation information about P. phenolica phages in the genome databases may not be sufficient for the functional prediction of their encoded proteins. This is the first report of a P. phenolica-infecting phage, and this phage genome study will provide useful information for further molecular research on P. phenolica and its phage, as well as their interactions.