Heathrow said the number of passengers it carried last month was ahead of 2019 levels for the first time since the pandemic.
The airport said 7.1 million passengers travelled through one of its terminals in September.
It makes September the first month that numbers have been above pre-pandemic levels, but that is largely because there were strikes in September 2019.
Last month the business said that annual figures for this year will still be below pre-pandemic levels.
Compared with a year ago, there was a 22.4% rise in the number of passengers travelling through the airport.
The biggest increase (59.6%) was in passengers heading for or coming from the Asia and Pacific region, Heathrow said.
It added that around 358,000 passengers travelled within the UK, a 39% rise on a year earlier.
The lowest increase was in passengers going to and from the Middle East, up just 11.4% to 686,000.
Heathrow reached the milestone in the last monthly update overseen by chief executive John Holland-Kaye.
Mr Holland-Kaye will hand over the job to Thomas Woldbye on October 18 after being in charge for nearly a decade.
He said: “It has been a privilege to lead the very talented team which, in less than a decade, transformed Heathrow into a hub airport that the whole nation can be proud of.
“We have built a solid legacy for my successor – Heathrow is now a customer service business, with a clear path to net zero by 2050 and a plan to grow and to connect all of Britain to global growth.”
