Online food delivery (OFD) platforms guarantee access to food during the coronavirus disease 2019 (COVID-19) pandemic when commercial food establishments are closed and access to food retail is controlled. The present study aimed to describe the advertisements published in an OFD platform in Brazilian capitals, during the 13th and 14th weeks of the pandemic. Data collection occurred on 1 d of the week and 1 d of the weekend and during lunch and dinner time. A random sample of 25 % of the advertisements (n 1754) published in this period was classified in accordance with the presence of food groups and to the use of marketing strategies. Sandwiches, ultra-processed beverages, traditional meals or pasta were the most common food groups shown in the advertisements. Free delivery prevailed in advertisements of ice cream, candies or salty packages snacks and pizza (P < 0·01). Combos were more frequently shown in the advertising of natural juices or smoothies, ultra-processed beverages, sandwiches and pizzas (P < 0·01). Messages about healthiness were more seen among natural juices or smoothies, vegetables and traditional meals and pasta advertisements (P < 0·01) and less seen in sandwiches (P = 0·02) and pizza advertisements (P < 0·01). Economy messages were rare in advertisements of traditional meals or pasta (P < 0·01) and more common in ultra-processed beverages (P = 0·03) and ice cream, candies or salty packages snacks (P < 0·01) advertisements. The OFD platform promoted unhealthy eating during the COVID-19 pandemic in Brazil due to the expressive presence of unhealthy foods advertising.