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7 September 2015 Last updated at 16:34 BST
He said the refugees will come from camps bordering Syria rather than those who are already in Europe.
Pressure on the government to allow more refugees to come to the UK has intensified in recent weeks as questions about what to do with the huge numbers of migrants and refugees coming into Europe.
It's after tens of thousands of people, from places like Syria, Afghanistan, and parts of Africa, have come to Europe in the hope of a better future.
In a speech to the House of Commons Mr Cameron said Britain had a duty to help people in need.
The Prime Minister David Cameron has announced that Britain will take an extra 20,000 refugees as part of the response to the growing migrant crisis in Europe.