Like-for-like sales were down 3.7 per cent for the year to June 24. The second-half performance was better than the first, with like-for-likes down 1.8 per cent and 4.8 per cent respectively.
The group said it had a strong Easter after increasing investment in product and packaging.
However, commercial sales to other retailers decreased 10.7 per cent from£35 million to£31.2 million.
At e-commerce business, Thorntons Direct, sales were up 6.4 per cent from£5.2 million to£5.5 million.
Chairman John von Spreckelsen said: 'Thorntons sells excellent chocolates and ice creams. We need to focus on convincing more customers to buy these quality products.'
There was speculation in the weekend press that the Thorntons retail division could be split from manufacturing if private equity group Baugur takes over the company. The Icelandic investment firm are in the early stages of talks to buy the chain and are believed to be planning to sell the group's Derbyshire factory to Swiss chocolate maker Lindt.
The group also appointed operations director Barry Bloomer to the board. Bloomer joined the company in July last year from Black & Decker, where he was European operations director.
Thorntons chief executive Peter Burdon said: 'Barry has made a significant impact on our manufacturing, sourcing and distribution activities in his year with Thorntons and I am delighted to welcome him to the board.'