Taiwanese lesbians have been found to utilize screening tests for breast cancer at lower rates when compared to women in general in Taiwan. However, there is a lack of evidence regarding the factors which influence Taiwanese lesbians' breast healthcare behaviour and intentions. A two-phase sequential exploratory mixed-methods study was employed to explore the factors influencing Taiwanese lesbians' breast healthcare behaviour and intentions, including semi-structured interviews and an online survey. Taiwanese women aged 20 years or above and who self-identified themselves as lesbians or as partnered with the same gender were targeted and recruited, using purposive and snowball sampling. Thirty-seven semi-structured interviews were conducted initially. According to the interview findings and two existing health psychology models (the health belief model and the theory of reasoned action), a questionnaire was developed and an online questionnaire survey was undertaken with a larger population. A total of 284 women completed the online survey.The findings showed that the lesbians' breast healthcare behaviour and intentions were directly or indirectly affected by their gender identity, gender role expression, patient-provider interaction and partners' support. In addition, it was also found that the lesbians may share similar views about breast cancer and breast cancer screenings, self-efficacy and cues to action with women in general in Taiwan. Some of these factors had an important effect on the lesbians' breast healthcare behaviour and/or intentions, in particular the perceived barriers to performing and/or having breast cancer screenings, the perceived susceptibility to breast cancer, self-efficacy and cues to action.Based on the PhD findings and social-ecological model, four levels of recommendations were proposed in order to encourage Taiwanese lesbians' utilization of breast cancer screenings and to promote their breast health.