BACKGROUND: Despite numerous benefits of exclusive breastfeeding (EBF) for infants and mothers, a significant decrease in the EBF rate in the USA at six months compared to the rate at birth suggests that reasons for initiation and continuation of EBF may differ. The purpose of this qualitative study was to explore psychosocial factors underlying the continued EBF behaviour for six months, in order to identify salient belief structures according to the theory of planned behaviour. METHODS: Participants were recruited from central Indiana in the USA. They were asked to respond to an open-ended questionnaire designed to elicit positive/negative consequences, approving/disapproving social referents, and easy/difficult circumstances in continuing EBF for six months. Responses were translated into behavioural, normative, and control beliefs of the theory. RESULTS: Findings suggest that respondents (1) value emotional and health benefits of continued EBF for six months; (2) feel the approval from family and friends but disapproval from the society; (3) view health professional's position as positive and negative. CONCLUSIONS: Breastfeeding educators can more likely improve the EBF duration by addressing these salient beliefs. Identified beliefs provide a basis for the development of a quantitative instrument to further study the EBF behaviour.