The study investigated factors that affect quality of education after the introduction of Subsidized Secondary Education (SSE) policy in Rongai Sub-County, Kenya. With the introduction of SSE, schools have registered over-enrolment, which means that instructional materials and teaching personnel available in schools could be constrained. One of the objectives of education in Kenya is equipping learners with knowledge, skills, values and attitudes. To be able to achieve this objective, the schools must have adequate learning resources. The adequacy of learning resources was obtained from principals and teachers. The study used Convergent Parallel Mixed Methods research design. The population comprised principals of the 39 schools that participated and 78 teachers (2 randomly selected from each of the 39 public secondary schools), giving a population of 117. Data were collected using questionnaires and interview schedules. Quantitative data were analyzed using descriptive statistics, and thematic approach was used to analyze qualitative data. It has been established that factors that affect quality of education after the introduction of SSE can be categorized as inadequacy of personne, and instructional materials, administration, and politics. The findings will inform policymakers of factors affecting quality of education after the introduction of SSE.