TOKYO—Japan Airlines Co. said Thursday that its net profit more than doubled in the fiscal first quarter as international passenger traffic recovered from last year's March 11 disasters, canceling out rising costs and keeping the carrier on track for an expected initial public offering next month.

JAL said its net profit for the three months ended June 30 climbed to ¥26.9 billion ($343 million) from ¥12.7 billion in the same period a year earlier. The company's president, Yoshiharu Ueki, said the most recent results were...