Airports operator BAA said 3.8 per cent more people used its airports in January compared with the year before.
A total of 7.5m people went through BAA airports, with strong growth at Heathrow.
BAA saw a rise in passengers at five of its six UK airports, with only Stansted recording a fall last month.
BAA said Heathrow, criticised for its performance during the winter weather, had its best January since 2006.
Colin Matthews, chief executive, said the figures reflected an "improving economic environment".
Heathrow recorded an increase of 4.6 per cent to 5.05m passengers, although services in January 2010 were disrupted by bad weather.
BAA said in a statement that Heathrow had had it strongest long-haul performance in the airport's history, supported by growth on Chinese and Indian routes.
Air cargo, a reflection of international trade, remained strong, BAA said, with an 8.5 per cent overall increase at its airports and a 9.3 per cent rise at Heathrow.