There is limited understanding on female same-sex sexual relationships development in Tanzania. This study documents perceived reasons for female same-sex sexual relationships in Tanzania. Conducted a cross-sectional descriptive formative study in Dar es Salaam. Women who have sex with women (SSW) were recruited through snowball sampling and WSW’s organization leaders, community members were purposely recruited. Qualitative methods used to collect data: in-depth interviews (IDIs), focus group discussions (FGDs), collecting WSW’s life stories and observations of female same-sex sexual relationship-related issues. Twelve WSW participated in each FGD. We conducted IDIs with eight WSW, three with WSW’s organizations leaders, three with community leaders and one with a male (businessman) community member. Three leaders of groups supporting WSW were interviewed three times each to clarify on issues that emerged from IDIs, FGDs and observations. We applied thematic approach where open systematic coding of data in the participants’ language and combining emerging emic concepts with preconceived theoretical constructs was used. Thirty-nine individuals participated in this study. Reasons for developing sexual attraction between and among women included biological orientation, poverty, peer pressure, eroding African social norms and values, globalization and paid sex among women. Tanzanians hold varied reasons behind development and evolution of female same-sex relationships that have implications to the WSW’s health and well-being. We recommend for larger ethnographic and multidisciplinary studies, and nationally representative samples to assess the genetic, individual and socio-environment factors influencing onset and evolution of female same-sex sexual behaviors and practices in Tanzania.