The deep-water mysid crustaceans of Australia have been barely known. Recent explorations of RV Investigator (CSIRO) in the southeast Australian waters discovered a unique fauna. In this special study of the marine subfamily Boreomysinae (family Mysidae) in Australia, five species from both genera Boreomysis and Neobirsteiniamysis are reported, including two new species for science: B. inopinata sp. nov., B. sibogae, B. sphaerops, B. urospina sp. nov. and N. inermis. Among the members of the subfamily, only B. sibogae has been previously known from Australia. The genus Neobirsteiniamysis and its bipolar-amphitropical species N. inermis are firstly recorded in Australia. Boreomysis inopinata sp. nov. has additional spinules on the outer spine of the antennal scale, which are not found in other species of the subfamily. Boreomysis urospina sp. nov. has the longest first segment of the uropodal exopod, laterally terminated by three spiniform setae; and its uropodal endopod is armed with up to five medial spiniform setae, the largest number in the subfamily. This species is included in a newly established subgenus Petryashovia subgen. nov., which unites epi-mesopelagic boreomysines, lacking the rostral projection, having rather small ventrolateral lobes of the carapace, and the 1-segmented propodus of the pereopods. The subfamily and generic diagnoses are updated. Additionally, a fragment of the mtDNA COI gene was sequenced for most of the studied species.