The History Channel survey found 20 per cent didn't know Jesus birth was remembered on Christmas Day and one in 20 thought Jesus was born over Easter.
Around one in 10 were unable to name Bethlehem as Jesus' place of birth while another 10 per cent were unaware he was born in a stable, despite the prevalence of nativity plays and Christian teaching in schools.
A spokesman for the History Channel, which commissioned the research to mark the launch of its new show Robert Powell on The Real Jesus of Nazareth, told the Independent: "For many of us, Christmas is a festivity we all look forward to celebrating with our loved ones.
"But over time, it seems people are becoming more and more unaware about the real reason we mark the day and the story of Jesus."
Despite the confusion over why we celebrate Christmas, the researchers found more than seven in 10 believed they had a good knowledge of the story of Jesus.
The study of 2,000 adults revealed one in 20 couldn't name Mary and Joseph as Jesus' parents while 16 per cent didn't know Jesus' occupation was a carpenter and thought he was jobless.
The research, carried out via OnePoll.com, also revealed only three in ten learned their knowledge of Jesus and his story from The Bible itself.
Most people's knowledge of Jesus came from what they were taught in school and one in ten picked up their knowledge by watching TV shows.
