The genus Pseudoalteromonas of the class Gammaproteobacteria represents a ubiquitous clade of marine bacteria, and is known to be ecologically and evolutionarily influenced by phages. Here, we report the complete genome sequence of a Pseudoalteromonas phage (PHS3) and major findings from the genomic analysis. Morphological observation suggested that the phage belongs to the Siphoviridae family. Genome of phage PHS3 consisted of a linear, double-stranded 35.626 kb DNA molecule with 40.85% GC content, and 58 putative open reading frames (ORFs) without tRNA. Comparative genome analysis revealed that phage PHS3 is related to the Pseudoalteromonas phage pq0 (acc. no. NC_029100). They had a synteny in the structure and DNA replication/regulation module and shared many structural and replicate genes, while little similarity was found in the phage packaging module. Knowledge of this phage might be helpful for further research on the interaction between phages and their hosts.