Purpose Lifestyle factors might play a role in the development of breast cancer. This study aimed to examine the relationship between lifestyle factors and the risk of breast cancer in Vietnamese women. Methods This study included 370 newly diagnosed breast cancer cases and 370 age-matched controls recruited between September 2019 and March 2020 in Ho Chi Minh City. Breast cancer diagnoses were confirmed through pathological examination, while controls were randomly selected from a non-cancer population. Lifestyle factors, including smoking status, sleep duration, and physical activity level, were collected through a face-to-face interview. The association between lifestyle factors and breast cancer risk was analyzed using adjusted conditional logistic regression, and a case impact number (CIN) was calculated to determine the effect of these factors on breast cancer risk.. Results Passive smokers were associated with an almost two-fold greater risk of breast cancer compared to non-smokers (adjusted odd ratios 1.69, 95%CI: 1.09-2.63). The CIN was 4, meaning that passive smoking was a contributing factor to one out of every four breast cancer cases. Physical activity level and daily sleep duration were not significantly associated with breast cancer risk. Conclusion Passive smoking was associated with breast cancer in Vietnamese women, highlighting the potential for implementing a passive smoking prevention policy to reduce breast cancer.