Urban-poor households are disproportionately food insecure. The Status and Determinants of Food Insecurity and Undernutrition in Poor Urban Settings (SDFU) cross-sectional surveys were conducted in 2020-2021 to assess the impacts of COVID-19 on food security and diet quality among urban poor women of reproductive age (WRA) and children under 5 (CU5) in Jakarta, Quezon City, and Yangon. Data, collected on food insecurity and child and maternal diet quality using Computer Assisted Telephone Interviewing (CATI), were compared with prepandemic surveys. Prevalence for food insecurity and diet quality indicators were computed. Eight in 10 households in all three cities reported reduced incomes, with 6 in 10 worried about food the previous year. Over 10% of households in all cities substituted nutrient-dense (ND) foods with cheaper alternatives; yet less than 50% of children 6-59 months ate sugar-sweetened beverages or sweet and savoury snacks. Compared with baseline, women's minimum dietary diversity (MDD) in the three cities was significantly lower (up to 30% lower in Yangon and Jakarta), while the prevalence of children (6-23 months) meeting MDD was lower by 17.4%-42.5% in all cities. MDD was attained by >40% of children (24-59 months) in Yangon and Jakarta but only 12.6% in Quezon City. To improve food security and diet quality, multi-sectoral interventions are needed, including distributing ND foods and cash assistance to vulnerable households with CU5 and WRA and delivering targeted nutrition training to encourage appropriate complementary feeding practices and purchasing and consumption of ND foods.