"There are still a few issues that have to be settled," the French leader told Europe1 radio during an official visit to China.
"Yes, failure is still possible, but today I am confident," said Hollande.
The November 30-December 11 UN summit in Paris will be opened by world leaders, including US President Barack Obama, China's Xi Jinping and Narendra Modi of India.
The aim is to unite all the world's nations in a single agreement on tackling climate change, with the goal of capping warming at two degrees Celsius over pre-Industrial Revolution levels.
The agreement will be backed by a roster of national pledges for reducing greenhouse gas emissions blamed for global warming.
Hollande said it was encouraging that major emitters like China and the United States, as well as developing nations were all deeply engaged in the notoriously combative negotiating process.
Asked if he thought the conference would be a success, Hollande said: "It is possible, not certain."
Among the key points still in dispute, he cited $100 billion in annual climate finance that rich nations had promised for developing countries from 2020.
Some $65 billion has been secured and another $20 billion promised, said Hollande, but "we are not yet at $100 billion".
Yesterday, Hollande and Xi said the new agreement must include five-yearly reviews of nations' compliance with their own carbon-cutting undertakings.
They also agreed that the pact must be legally binding.
China is the world's largest greenhouse gas polluter and will be a key player at the Paris event.
It is an important member of the largest negotiating bloc, the G77 group of developing nations, which insists that rich nations must bear bigger responsibility for cutting emissions, since they have been polluting for longer.
Developed nations point the finger, in turn, at emerging giants like China and India burning massive amounts of fossil fuel to power their fast-growing economies and populations.
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