Understanding SME’s growth is critical to economic development. It is expected that SMEs exhibit faster growth rates than larger counterparts. It is therefore important to gain a greater understanding as to what shapes growth and expansion especially in Small and Medium-size Enterprises. This Study examines the internal factors affecting growth and expansion of SMEs in Kibera Slum, Nairobi. Specifically the study sought to ascertain the factors that contribute to growth and expansion of SMEs in Kibera Slum, establish relationships between form of ownership and growth and expansion of SMEs in Kibera slum and determine the effect of level of education and managerial skills on growth and expansion of SMEs in Kibera Slum. The study established that form of ownership, educational and managerial skills of the owners and employees, location of the SME and access to financial resources are some of the internal factors that that affected growth and expansion of SMEs. The study findings will be of value to relevant managers of SMEs in Kibera, Policy makers, Scholars and financial advisers.