Resumen: Introduction: COVID-19 lockdown affects socioeconomics, health and food security, especially in a vulnerable population, due to the reduction of jobs, income and access to food. Objective: To determine food insecurity and prioritization of food purchases in household in lockdown during the COVID-19 pandemic in Chile. Material and methods: Observational analytical study. An online questionnaire was sent through social networks, which included socio-demographic information, priority of purchase of selected foods, less food at home and a scale of household food security. Results: 1,114 people participated, 87.8% of them were women, 80.9% of the participants had been in quarantine for 4 or more weeks. As the weeks of quarantine increased, mild food insecurity increased from 26.9% to 36.1% and moderate from 1.7% to 7.8%. Food security decreased from 70.6% to 55.7%. Between 49.2% and 55.5% of the participants, in the fifth week of confinement, prioritized dairy, rice/pasta, flour, legumes, oil, potatoes and 27.0% sugar/honey. Fresh foods such as fruits and vegetables were not prioritized. Conclusion: Lockdown generated a progressive increase in mild and moderate food insecurity. The prioritization of purchase in lockdown was characterized by foods with a longer shelf life, more consumption, easy to prepare meals and foods which are basic ingredients of other preparations. Fresh foods like fruits and vegetables were not prioritized. Prioritization was related to educational level.