Worldwide, ultra-processed food (UPF) consumption is rising. Children and adolescent are age groups most affected by the increased consumption of such products. The aim of this pilot trial was to develop a health promotion intervention that increases literacy on UPF among Portuguese adolescents. A public school from the district of Porto was chosen by convenience. From the 10 total classes (242 students) registered in the seventh grade, the school management randomly selected 3 classes (74 students). This intervention was implemented in May/June 2021 in a faceto-face situation and involved an UPF booklet and its explanatory video, both developed to fulfil this trial objectives, and two literacy sessions about UPF identification and health implications of its consumption, also including ludic activities. To assess effectiveness, a questionnaire about UPF knowledge was applied at baseline and post-intervention. The sample consisted of 64 adolescents aged between 12 and 14 years (mean=12.75; sd=0.668). Most students were Portuguese (93.8%) and female (56.3%). Knowledge about UPF increased from 4.2% at baseline to 39.3% in the final stage of the intervention (p<0.001). This intervention showed to be effective by increasing students' knowledge on UPF. Additional intervention studies on this thematic should be performed in order to enhance literacy and facilitate conscious about healthy food choices.