This species is known from a fewer than five locations and, based on current known occurrences, it may have a small extent of occurrence (the current calculated EOO is 2,937 km²). It is potentially at risk of continuing loss of habitat. It could therefore qualify as threatened under criterion B, but the limits of its distribution are not completely clear and there have not been any long-term, comprehensive surveys in the area. It is possible that its distribution and extent of occurrence is significantly larger, which would potentially qualify this species for listing as Least Concern. Therefore, it is considered more appropriate to assess this species as Near Threatened, as it is likely to at least be approaching the thresholds of criterion B. Further research into its ecology, population and threats is needed.

Rattus vandeuseni is restricted to the mountains of south-east Papua New Guinea, where it is found at altitudes above 1,300 m asl. It is currently only known from specimens collected in the 1990s from Milne Bay Province on the slopes of Mt. Dayman, near Param and Munimun Village. Cole et al. (1997) described it as “presumed endemic to mid-montane forests of the eastern Owen Stanley Range”. Further survey work might reveal a wider distribution (e.g., it is possibly present on Mt. Simpson). It appears to replace the closely related but more widespread R. verecundus at around 1,300 m asl (Aplin et al. 2003). Its range is suspected to be very fragmented.

Very little is known about its population. It may be locally abundant at certain sites but absent from others. At least 40 specimens have been collected.

Individuals have been recorded in primary montane tropical moist forest. This species’ original locality was characterised as an oak forest with many large trees over 30 m tall, as well as numerous dead trees covered by ferns and mosses, and regular mists (Taylor et al. 1982). It may be more tolerant of disturbed valley habitat than its congeners such as R. verecundus (see Cole et al. 1997). The only specimen captured by Cole et al. (1997) was found with burgundy-stained fur, indicating contact with fruit, and others have been trapped with the use of peanut butter, beetle larvae and sweet potato baits (see Burgin 2017). Overall, little is known about the natural history of this species.

The forest within which this species lives has been degraded in parts of its range. From 1972–2002, 14,456 ha of highland forest was degraded in the south-eastern forests of Papua New Guinea (Shearman et al. 2009). Forest loss in Papua New Guinea is largely driven by subsistence agriculture and oil palm plantations, some of which is being pushed to higher elevations as lowland plantations expand and human populations increase (Gamoga et al. 2021). It is not known to what extent this species tolerates habitat change or degradation. Additionally, there may be competition with Rattus rattus at the lower edges of its elevational range.

It is not known if the species is present in any protected areas. Further studies into the distribution, natural history, habitat status, and threats to the species are needed. Important areas of habitat for this species should be identified and protected.