Pro-Palestine and anti-colonial messages were scrawled across the memorial in red paint at Anzac Park overnight.
The Australian Vietnam Forces National Memorial was constructed in 1992 and pays tribute to Australians who served in Vietnam from 1962 to 1973.
Vandals sprayed messages in red paint on the memorial, in what appeared to be a protest against the conflict and growing humanitarian crisis in Gaza.
The words "eyes on Rafah", "eyes on Gaza", and "this is genocide" were written on the structure.
The images were shared with Nine radio station 2GB.
The vandals also spraypainted the words "the colony will fall", echoing the sentiments of other acts of anti-colonial vandalism across the country in recent weeks.
A James Cook statue was sawn off at the base in Melbourne late last month, with images of the vandalism posted online with the same message.
A spokesperson from ACT Policing said police were aware of the vandalism.
"Police remind the community that peaceful protest is part of healthy democracy, however criminal acts will not be tolerated," they said.
