Billionaire Microsoft co-founder Bill Gates met Prime Minister Julia Gillard in Canberra this morning to lobby for an increase to Australia's $5 billion overseas aid budget.

The meeting kicked off a hectic day for Mr Gates, who will also speak at the National Press Club in Canberra at lunchtime, meet with Opposition Leader Tony Abbott, and take part in a special ABC TV Q&A program tonight.

Speaking on Radio National Breakfast, Mr Gates thanked Australians for their generosity in raising the aid budget, but said more could be done.

"Australian aid is spent on a lot of very important, effective things, like health," he said.

But he said he was saddened by Australia's decision to defer increases in aid as part of this month's budget.

"When that got slowed down I was a little disappointed," Mr Gates told Radio National.

"But it [the aid budget] has been increasing and people should feel good about that."