The BAA airport saw a 2.8% drop but numbers at Aberdeen and Glasgow rose.
Aberdeen Airport saw the biggest boost with a 10.2% increase on March 2011. BAA said the increase reflected the rise in domestic traffic related to the oil industry.
At Glasgow Airport, passenger numbers for March 2012 were up 4.6% on the same month last year.
The airport handled 507,600 passengers last month while 700,000 passed through Edinburgh Airport.
The Capital’s airport said it was expecting the drop.
A spokesman said: “Passenger numbers are on forecast. That drop in passenger numbers is mainly based around the fact that Ryanair’s winter schedule took some passenger numbers away from us. That has been constant over the past three or four months.
“We are hopeful as we move to summer schedules that our figures will pick up.”