The attack took place at Lion Park near Johannesburg, reported The Independent.
According to media reports, they may have been travelling in a car though the park with its windows open.
"The lion appears to have jumped into the car and bitten the woman," said Scott Simpson, a manager at the lion park.
He added that the man was injured trying to protect the woman.
"Our staff working at the top of the camp tried to get the lion away from the car. Ambulances were called immediately but it was too late," Simpson said.
Visitors to the park are told not to leave their windows open.
"We put signage up everywhere that people must keep their windows closed. We hand them a slip of paper when they enter the park, I really don't understand why people think its okay to leave windows open."
The attack is the third at the park in the past four months.