Aim Breastfeeding is believed to be beneficial to both mother and child. Although the percentage of Polish mothers who start breastfeeding after childbirth is relatively high, most of them finish after 8–12 weeks. Many factors are involved in the decision to stop, including an unfavourable social attitude towards breastfeeding in public. Our cross-sectional web-based study was conducted to identify the factors predicting negative attitudes towards public breastfeeding among Polish women. Subjects and methods A population-based internet-administered public opinion survey was conducted among 663 women aged 19 to 50 years old regarding their attitude towards breastfeeding in public. The participants completed a questionnaire concerning demographic data, general beliefs about breastfeeding and attitudes towards breastfeeding in public. Results Overall, 46.6% of respondents had a negative attitude towards breastfeeding in public. Multivariable logistic regression analysis found that the beliefs that breastfeeding is not a natural activity [adjusted odds ratio (AOR) = 17.54; 95% CI = 1.44–21.95] and that breastfeeding is not emotionally moving (AOR = 8.73; 95% CI = 3.950–19.30) or not having any opinion (AOR = 2.31; 95% CI: 1.18–4.50) to play the most significant roles in shaping a negative attitude, as well as breastfeeding their own child for < 6 months (AOR = 13.93; 95% CI = 0.14–20.24). Conclusions As women’s beliefs about breastfeeding play a key role in choosing to breastfeed in public, there is a need to further explore attitudes regarding this activity.