This paper examined the number of qualified teachers and its relationship to students' academic performance in public secondary schools in a sample of Local Government Areas (LGA) of Osun State. This descriptive study used a post-hoc dataset. An instrument titled “Quantity and Quality of Teachers and Students' Academic Performance” (QQTSAP) was used for the study. Twenty-one (21) public secondary schools, one in each LGA from a population of thirty-one (31) LGA in the State, were sampled. The Senior School Certificate Examination results from 2000/01 to 2004/05 were used to analyze students' academic performance and reflected some concerns in the school system. The data were analyzed using ANOVA and Spearman rank correlation coefficient to test the three operational hypotheses. Findings of this study showed teachers’ qualifications, experience and teacher–student ratio were significantly related to students’ academic performance. These findings can be used to guide planners about the need for qualified teachers to facilitate effective teaching and learning in secondary schools in Nigeria.