AlthoughAlteromonasis ubiquitous in the marine environment, very little is known aboutAlteromonasphages, with only ten, thus far, being isolated and reported on. In this study, a novel double-stranded DNA phage,Alteromonasphage P24, which infectsAlteromonas macleodii, was isolated from the coastal waters off Qingdao.Alteromonasphage P24 has a siphoviral morphology, with an icosahedral head, 61 +/- 1 nm in diameter, and a tail length of 105 +/- 1 nm.Alteromonasphage P24 contains lipids. It has an optimal temperature and pH for growth of 20celcius and 5-7, respectively. A one-step growth curve shows a latent period of 55 min, a rise period of 65 min, and an average burst size of approximately 147 virions per cell.Alteromonasphage P24 has the genome of 46,945 bp with 43.80% GC content and 74 open reading frames (ORFs) without tRNA. The results of the phylogenetic tree, based on themcpandterLgenes, show thatAlteromonasphage P24 is closely related toAeromonasphage phiARM81ld. Meanwhile, phylogenetic analysis based on the whole genome of P24 indicates that it forms a unique viral sub-cluster withinSiphoviridae. This study contributes to the understanding of the genomic characteristics and the virus-host interactions ofAlteromonasphages.