Former prime minister Scott Morrison approved grants in response to Russia's invasion of Ukraine before the spending was known to have met government rules.
The auditor-general on Thursday released a review of how Defence handled Australia's assistance commitments, finding the department's overall response was largely effective.
The report said Defence provided "timely, relevant and coordinated advice" to its senior leaders, the defence minister and the government.
However, the audit raised questions about whether grants had the proper legal authority.
On February 23, 2022 - the day Russia invaded Ukraine - the prime minister approved an unspecified payment to NATO's Comprehensive Assistance Package Trust Fund for Ukraine.
A day later, Defence provided advice to then defence minister Peter Dutton, who on February 25 approved a $4.2 million grant for the NATO trust fund.
The report found Defence was at least "medium to high risk" of not having the appropriate legal authority for the making of payments.
While acknowledging Defence had to deliver aid "quickly" to Ukraine, the audit found it could not demonstrate all government policy approvals had been provided for $36.4m worth in military assistance sent over last year.
In addition, 58 items worth $38.4m were transferred to the Ukrainian government without being included in a written exchange between the two countries.
"Defence's development and implementation of Australia's approach to providing military assistance to the government of Ukraine was largely effective," the report said.
"Defence delivered military assistance quickly and in line with Australian Government expectations, while assessing the risks and implications for Australian national interests and capability.
"However, not all legislative and administrative requirements were met in the context of this rapid implementation activity."
The audit found certain items before being sent to Ukraine did not have an Australian Defence export permit, gifting authorisations under the relevant act, or lodged Australian customs export declarations.
"Defence has not effectively accounted for gifted assets by taking appropriate action to record the disposal of gifted equipment in its records," the report said.
Prime Minister Anthony Albanese announced earlier this week the latest assistance package worth $110m, bringing Australia's total contribution to Ukraine to $790m.
In its response to the audit report, the Defence department agreed with the improvements and said it will "evaluate all aspects of its delivery of military assistance to the government of Ukraine".
"In mid-2022, Defence established a regular consultation process to discuss current and future gifting activities including identifying process, approvals and delivery," the department said.
