Gap international like-for-likes, which includes the UK, were down 4% in the key Christmas trading period in the five weeks to January 1.
For the group, like-for-like sales were down 3%. The drop compares with a 2% rise for December 2009. Gap North America was the hardest hit with like-for-likes down 8%.
Net sales for the period equalled the previous year figure at $2.0bn (£1.29bn).
Gap Inc chief financial officer Sabrina Simmons said: “After a strong start to the holiday season in November, sales and traffic trends for our brands were less consistent in December.
Like-for-likes for the 48 weeks to January 1 were up 1%. Total sales were $13.82bn (£8.89bn), up 3% year-on-year.