Objectives. The mechanisms underlying the protective effect of breast-feeding on the development of childhood overweight are unclear. This study examines the association of breast-feeding with weight gain in the first year, and body mass index (BMI) and overweight up to 4 years. In addition, we examine possible mechanisms of this effect (i.e., feeding pattern, eating style, unhealthy snacking behavior). Methods. Data originated from the KOALA Birth Cohort Study (N = 2 834). Questionnaires assessed breast-feeding duration up to 12 months, feeding pattern (i.e., feeding on demand or feeding to schedule) at 3 months, BMI at 1, 2 and 4 years, eating style (e.g., slow eating) at age 1, and unhealthy snacking at age 2. Linear and logistic regression analyses were used to examine the association of breast-feeding and feeding pattern with eating style, unhealthy snacking, BMI z-scores and overweight. Results. Each additional month of breast-feeding was associated with less weight gain in the first year (regression coefficient B = −37.6 g, p < 0.001), a lower BMI z-score at age 1 (B = −0.02, p < 0.01), and a lower odds of being overweight at age 1 (odds ratio = 0.96, p < 0.05). Breast-feeding was associated with fewer unhealthy snacking occasions per week at age 2 (B = −0.19 for each month of breast-feeding, p < 0.001), but was unrelated to eating style. Feeding pattern was unrelated to all outcome variables after adjustment for breast-feeding duration. Conclusions. The study showed a short-term protective effect of breast-feeding against overweight development. Possible mechanisms through which breast-feeding may protect against overweight include less unhealthy snacking behavior, but not feeding pattern or child's eating style.