By position, deputy principals (DP) are middle level school leaders who are anticipated to be appointed as future principals. Nevertheless, previous studies proved that DPs receive low levels of support in terms of their leadership knowledge and skills. Thus, in assisting DPs as their mentors, principals have a significant role within the informal leadership mentoring practices supporting DPs' informal professional development. In this study, we explored the guidance principals use to assist their DPs. This mixed method study of 318 DPs from Malaysian primary schools examined their experiences of principals' informal mentoring and guidance. In addition, using semi-structured focus group interviews, 11 DPs were interviewed to obtain in-depth experiences of principals' informal mentoring. It was revealed that primary school DPs felt satisfied and assisted with the guidance and advice provided by their principals through sharing knowledge and being a source of reference.