He was referring to a proposal by Brazilian President Luiz Inacio Lula da Silva, who is expected to seek Annan's backing for a global fund against hunger when they meet in Geneva on Friday.
Lula proposed the hunger fund at a G8 summit in France last June, saying it could be financed by a tax on arms sales, or by countries handing back a percentage of debt repayments they receive from poor countries.
"I would be delighted if we can do that," Annan on Thursday told a news conference in Brussels, when asked if he would favour a global tax.
"Not only would it be extremely helpful for the kind of work we do, but it will help millions if not billions around the world," he said.
"But I think there's going to be a real struggle. There are governments who see this as taxing their citizens, and believe only they can tax their citizens."
Annan noted that the idea was not new, adding: "This is a real challenge. I think we need to explore all creative ways of raising funding for development."
"But I think there's going to be a real struggle. There are governments who see this as taxing their citizens, and believe only they can tax their citizens"
The UN secretary-general will head to Geneva on Friday - where he will also meet French President Jacques Chirac - on the last leg of a European tour. He arrived in Brussels on Wednesday.
Malaysia's outspoken former prime minister Mahathir Muhammad has also called for a worldwide tax, targeting multinational companies, saying it would be "morally desirable" to tax the rich to help the poor.