Some 12 countries have reportedly agreed to adopt the measure.
The tax is to be imposed by Brazil, Chile, Cyprus, Congo, France, Ivory Coast, Jordan, Luxembourg, Madagascar, Mauritius, Nicaragua and Norway, said French officials on Wednesday at the end of the two-day conference gathering representatives from 95 countries.
In addition, Britain, while not introducing a new tax, will divert money from an existing surcharge on air travel to the same end: combating Aids, tuberculosis and malaria in poor countries, especially Africa.
French officials called the conference a success in getting other countries to adopt the idea championed by Jacques Chirac, the French president, despite the small number of states that have joined so far and the hesitation of other big Western countries with high numbers of airline passengers.
The United States opposes the plan, as does the airline industry and business groups, fearing it would burden carriers already struggling with high oil prices and fierce competition.
But Kofi Annan, the UN secretary-general, speaking at the opening of the conference on Monday, hailed the initiative.
The new tax is expected to raise
$237 million per year
But, as Annan and Chirac pointed out, governments' pledges are falling short of the money promised, requiring new ideas to come up with the funds, such as the airline tax.
France will in July be the first country to apply the new tax, which will add one to 40 euros ($1.2 to $47) to the price of air tickets, depending on the distance travelled and the class of seat. That is expected to raise 200 million euros ($237 million) per year in development aid.
Philippe Douste-Blazy, the foreign minister, said the money would go to a central medicine buying facility France and Brazil are working to set up which would notably work to give Aids and HIV sufferers cheaper and easier access to anti-retroviral drugs.
Forty countries back the idea of the new facility, he said. "In other words, this is irreversible."
The United States, again, is hostile to that idea and was only present at the conference in the status of observer, not participant.
But Peter Piot, the head of the UN agency fighting Aids, said he was optimistic about the moves sponsored by France and Brazil.
It was "absolutely necessary" for countries to come up with new ways of raising development aid, he said, but only "on condition that that is not a pretext for states to reduce their contributions elsewhere".