German flag-carrier has reported a loss of €336 million for the first three months of the year.
The carrier, the largest in Europe, was hit by rising fuel costs and overcapacity in Europe.
Shares in the company fell slightly in response, down to €21.82 this morning.
Lufthansa said a €202 million rise in fuel costs had contributed to the loss.
Unit revenues at Lufthansa-owned airlines, including Swiss, Austrian Airlines and Eurowings, also fell significantly in the period.
Lufthansa reported an operating profit of €52 million for the same period a year earlier.
European airlines are battling overcapacity and high fuel costs, while uncertainty around Brexit has led to some travellers to delay booking summer holidays.
Lufthansa said it expects revenues in constant currency terms to improve in the second quarter as booking levels recover, adding that for 2019, it still expects to make an adjusted operating profit margin of 6.5-eight per cent.