Heathrow saw a 4.8% year-on-year decline in passenger numbers in February due to coronavirus.
The UK’s busiest airport said the fall to 5.4 million passengers was driven by lower demand on Asian and European routes.
The figure takes into account the extra day last month as 2020 is a leap year.
Heathrow warned that demand has continued to weaken in March.
The airport’s chief executive, John Holland-Kaye, said: “The threat of coronavirus is an increasing challenge for the UK.
“We are working day and night to ensure Britain’s front door is open and safe for our people and passengers.
“We will continue to work with the Government to limit the impacts this will have on UK plc.”
The impact of coronavirus on global trade is highlighted by the amount of cargo passing through Heathrow last month falling by 9.5% to 115,900 metric tonnes.
Airlines have cancelled thousands of flights due to the drop in demand for air travel.
British Airways – the largest airline at Heathrow – has stopped flying to mainland China and Italy while frequencies have been slashed on other routes.