Based on high transmissibility of coronavirus disease-19 (COVID-19), nationwide lockdowns were undertaken to halt the spread of virus associated with changes in snack behavior. This study aimed to observe changes in snack behavior in Sri Lankan adults. This cross-sectional study was conducted from 27^th May to 02^nd June 2021. A pre-tested, self-administered questionnaire was shared via online social networking platforms using Google forms. Totally, 3601 respondents participated in the study, of which 60.1% were females, and 82.1% were Sinhalese. The majority of the respondents increased consumption of coffee/tea (53.7%), and biscuit (42.3%); where a substantial proportion reported decreased consumption of cake (49.8%), sweets (49.0%), snacks (47.5%), desserts (46.2%), and sugar-sweetened beverages (48.7%). Participants of 31-35 years age (OR=1.445; 95% CI: 1.119-1.865, p=0.005) and 36-40 years age (OR=1.409; 95% CI: 1.065-1.864, p=0.016) reported the significantly higher biscuit consumption. Respondents in 31-35 years age (OR=1.265; 95% CI: 1.004 to 1.592, p=0.046) significantly increased coffee/tea intake. Among ethnic groups, Sinhalese (OR=1.509; 95% CI: 1.164 to 1.955, p=0.002) and Tamils (OR=1.408; 95% CI: 1.007 to 1.969, p=0.045) showed significant odds to increased coffee/tea drinking pattern. The respondents with monthly family income levels of less than 200,000 LKR (1000 USD) significantly liked to report increased consumption of biscuits and coffee/tea. COVID-19 lockdown impacted snack consumption behavior among Sri Lankan adults. The consumption of coffee/tea and biscuit increased too.