Abstract Background To examine the proportion of healthier and less healthy food promotions in circulars of major Belgian supermarket chains. Methods Food promotions were collected from all circulars over 1 year from the five largest Belgian supermarket chains. Foods promoted were classified according to the World Health Organization Europe nutrient profile model categories and the level and purpose of processing as per the NOVA classification. In addition, promotional characters (i.e. cartoons, licensed characters, celebrities) and premium offers within the promotions were analysed. Results In total, 15,271 food promotions were analyzed. The most frequently promoted foods in circulars were processed meat, poultry and fish (11.8%); fresh and frozen fruit, vegetables and legumes (9.5%); soft drinks and sweetened beverages (9.0%); fresh and frozen meat, poultry, fish and eggs (8.6%); cakes, sweet biscuits and pastries (8.1%); ready-made and convenience foods (8.0%); chocolate and sugar confectionery; energy bars and sweet toppings (7.7%) and cheeses (5.7%). About 52.2% of food promotions across all circulars were for ultra-processed foods, with considerable variation across chains (42.9–61.6%). Promotional characters and premium offers were found within 5.3 and 19.5% of promotions respectively. For all chains, circular covers were healthier compared to entire circulars, with a lower proportion of ultra-processed foods and a higher proportion of fresh fruit and vegetables promoted. Conclusions Food promotions in circulars were most frequently for ultra-processed foods, with considerable variation across chains. Circular covers were healthier than entire circulars. Policies to reduce less healthy food promotions could contribute to improving the healthiness of supermarket food purchases.