Overall year-on-year traffic declined 1.2% last month, compared to August 2009, despite high passenger load factors.
Some 3,690,000 passengers flew through Gatwick in August, compared to 3,740,000 in the same month last year.
On average, 87% of seats were filled on flights from Gatwick last month, which the airport said represented a record passenger load factor.
Air transport movements in August fell by 3.7% year on year, which Gatwick said was due to "the full year impact of capacity consolidations on international markets".
International air transport movements fell 5%, while domestic markets rose 2.6%.
Flights to the north Atlantic saw the largest fall in the number of passengers (12.3%) through Gatwick, with Ireland close behind (10.4%).