This study aimed to examine individual-, household-, and community-level characteristics associated with nonexclusive breastfeeding (non-EBF) in infants younger than 6 months of age using Demographic and Health Surveys data collected between 2002 and 2005 in East and Southeast Asia. Multilevel logistic regression was used to estimate the odds ratios for factors associated with non-EBF. Exclusive breastfeeding rates in infants younger than 6 months were as follows: Vietnam, 15.5%; Timor-Leste, 30.7%; the Philippines, 33.7%; Indonesia, 38.9%; and Cambodia, 60.1%. The significant individual factors associated with non-EBF included first-born infants, working mothers, and higher maternal age. Communities with a higher proportion of wealthier households in Indonesia, trained delivery assistance in the Philippines, and poor maternal education in Vietnam and Cambodia were at greater risk for non-EBF. All countries need effort to improve EBF, specifically targeting working mothers, less educated women, rich households, and first-time mothers. Health institutions and care providers should be appropriately guided to support EBF.