The inflatable boats are worth $14 million and come just after Australia donated 49 Abrams tanks as part of a $250 million aid package.
"Ukraine has demonstrated its ability to thwart Russia's continued attacks from the Black Sea," Defence Minister Richard Marles said.
"We are proud to contribute to these vital maritime defences with this new package."
The boats would be useful on the front lines including in areas like Kherson, which was liberated in November 2022 but where Russian forces remain on the other side of the river, Ukrainian Ambassador Vasyl Myroshnychenko said.
"These are very good, they're very fast, rigid - I tested them in Tasmania and they can do some magic in terms of manoeuvrability and speed," he told AAP.
Inflatable boats have previously been given to Ukraine as part of a $100 million package announced in April.
Australia has contributed more than $1.3 billion in military support in total, including 120 Bushmaster protected infantry vehicles, artillery and ammunition.
Ukraine has requested Tiger helicopters that are set to be retired by Australia.
The Australian Defence Force previously buried its faulty Taipan fleet despite Kyiv asking for the choppers.
Defence Industry Minister Pat Conroy said the defence force was working through the Tiger's disposal plan and the federal government was in contact with Ukraine about continuing support.
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