Low transition rate of seminarians from Minor Seminary schools to Major Seminary schools for priestly formation has translated to an inadequacy of priests for serving the church and the society. This poses a challenge to the Catholic Church that depends entirely on ordained priests from the Major Seminaries to carry out its evangelical functions. Studies in secular institutions have shown that family-related factors had major influence on learners' transition rates. However, little research has been done to examine the influence of such family-related factors on transition of seminarians in seminary schools. This study thus sought to investigate the influence of family factors on transition rates of seminarians from Minor to Major Seminaries in Kisumu Ecclesiastical Province, Kenya. It targeted all the five rectors and 1075 former seminarians of the period 2014-2018 in all the five Minor Seminaries in the Ecclesiastical Province of Kisumu. The study was guided by Vygotsky's socio-cultural theory of development. The study employed aexplaratory mixed methods design. stratified simple random sampling were used to sample rectors and former seminarians respectively. Questionnaires,document analysis guide and observation schedule were used to collect data, which was then analyzed by frequencies, means and percentages. The finding were that; Transition rate of seminarians was significantly affected by family culture and traditions, and family decisions and preferences. The study recommended that the government should financially support genuine seminarians who may not afford the fees; the Catholic Church should have clear formation programmes and goals in the Minor Seminaries, and provide priests to teach, form and accompany the students in and out of the seminary; the rectors should perform thorough orientation interviews during selection of seminary entrants, and work towards having good role models in the seminary. Families should be encouraged to have good family (sacramental) catechesis. This would help meet the need for enough well-trained and dedicated priests in the Catholic Church, that may translate to the betterment of entire society.