: Lockdown measures were implemented in many countries to limit the spread of the COVID-19 pandemic. However, such restrictions could precipitate unintended negative consequences on lifestyle behaviors. The main objective of this study was to investigate the prevalence and determinants of unhealthy behavior changes during the COVID-19 lockdown among residents of the United Arab Emirates (UAE). : A cross-sectional web-based survey of adults residing in the UAE was carried out during lockdown (n = 2060). Using a multi-component questionnaire, the collected data included questions regarding the following lifestyle changes: Increased dietary intake, increased weight, decreased physical activity, decreased sleep, and increased smoking. An unhealthy lifestyle change score was calculated based on the number of unhealthy lifestyle changes each participant reported. In addition, sociodemographic and living conditions information was collected. Descriptive statistics as well as simple and multiple linear regression analyses were used to examine the prevalence and determinants of the unhealthy lifestyle changes considered in this study. : Among the unhealthy lifestyle changes examined, increased food intake was the most common (31.8%), followed by decreased physical activity (30%), increased weight (29.4%), decreased sleep (20.8%), and increased smoking (21%). In addition to identifying the correlates of each of the aforementioned lifestyle changes, the results of the multiple regression linear analyses revealed the following correlates for the overall unhealthy lifestyle change score: females (β = 0.32, CI: 0.22; 0.42), living in an apartment (β = 0.12, CI: 0.003; 0.23) and being overweight/obese (β = 0.24, CI: 0.15; 0.32) had higher scores, while older adults (>40 years) had lower scores (β = -0.23, CI: -0.34; -0.12). : The COVID-19 lockdown has resulted in a high prevalence of unhealthy lifestyle behaviors and practices among UAE residents. The findings of this study provided the evidence base for officials to design interventions targeting high-risk groups and aiming to improve healthy lifestyle factors among residents during the pandemic.