The decline worsened over the summer and into September, "reaching 20 percent" compared with the same period last year, CEO Nicholas Houze told a press briefing.
While July sales helped the figures, August "was a lot quieter... and September remains difficult," he said.
The January-to-June period saw a 5.9-percent drop in turnover for the chain, from 1.7 billion to 1.6 billion euros, Houze added.
Visitors from China, Taiwan and the United States normally account for half of the company's turnover.
But a string of terror attacks seems to have dented France's appeal among tourists, with the number of arrivals falling around 8 percent this year compared to 2015, the foreign ministry said Tuesday.
Houze said he was confident that foreign shoppers would return, since "Paris is still a dream destination".
Meanwhile Galeries Lafayette's Beijing store, opened in 2013, enjoyed a 15-percent increase in turnover to around 100 million euros in the first half of the year, Houze said.