Dollar Tree reported a 2.6 percent fall in quarterly profit as costs increased.
Net income fell to $121.5 million, or 59 cents per share, in the second quarter ended Aug. 2 from $124.7 million, or $1.25 per share, a year earlier.
Revenue jumped 9.5 percent to $2.03 billion.
Wall Street analysts had expected Dollar Tree revenue of $2.01 billion, according to a consensus estimate from Thomson Reuters.
Same-store sales rose 4.5 percent on a constant-currency basis. Analysts on average had expected a 2.5 percent rise, according to research firm Consensus Metrix.
Read MoreFamily Dollar rejects Dollar General bid, backs rival
Dollar Tree is a discount retailer that has a large selection of items that cost $1 at more than 5,000 stores in the U.S. and Canada.
Last month, Dollar Tree announced plans to acquire Family Dollar for $8.5 billion. The deal was expected to close by early next year and would result in a combined more than 13,000 locations. The company said it expects sales of more than $18 billion from the transaction, expanding the customer base from suburban America to Family Dollar's urban and rural locations.
This week, Dollar General made a competing offer of $9.7 billion for Family Dollar.
Check what markets are doing here.
—By Reuters with CNBC