Teacher mentoring is one of the most well-known and widespread methods of personalized guidance and support for school's new-entrant substitute teachers (Bezzina, 2006; Andrews & Quinn 2005; Moyles, Suschitsky & Chapman, 1999; Nemser-Feiman, 1996), providing multiple benefits (Ingersoll, 2003; Ingersoll & Kralik, 2004; Lambeth, 2012). However, in the Greek context, teacher mentoring as a practice, although it is institutionalized in 2010, has not been yet implemented. For that reason, the purpose of this study is to investigate whether school's new-entrant substitute teachers receive mentoring support and guidance, even informally, from their colleagues (peer mentoring) and their principal. Additionally, it explores the role of leadership in mentoring support as described above. A quantitative research approach has been adopted. Self-administered questionnaires were completed by 120 school's new-entrant substitute schoolteachers using the convenience sampling technique. The questionnaires included a Likert type scale with 51 items measuring different aspects of teachers' views about their informal peer mentoring support (Huling-Austin & Murphy, 1987) and leadership style of their principal (Organizational Climate Descriptive Questionnaire- Hoy & Clover, 1986). According to the results, school's new-entrant substitute teachers seem to receive in a small extent informal mentoring support and guidance from their colleagues and principal. However, colleagues provide to a greater extent mentoring support than school principals. In addition, school leadership, especially supportive leadership style is positively correlated with mentoring support.