This study investigated school size and facilities as correlates of junior secondary student s academic performance in Oyo state, Nigeria. An ex-post-facto descriptive survey stra .. research design was adopted stratified random sampling technique was used to select 53 out of the 304 public secondary schools in Oyo state. A total of 371 respondents made up of 318 teachers and 53 principals were involved as samples for the study. Two instruments used were: principals participating questionnaire and Teachers Participating Questionnaire (TPQ). The data collected were subjected to multiple regression analysis. The study found that the two independent variables (school size and facilities) contributed 52.27% (R2 = 0.5227) and 59.6% (R2 = 0.5967), respectively to the variances of junior secondary school student s academic performance. Two of the variables of school size and six of the variables of facilities have significant (p<0.05) contributions to the explanation of junior secondary school student s performance. Based on the finding of this study, it was recommended that more buildings should be provided in the secondary schools. The dilapidated ones be renovated and the damaged furniture be repaired to provide accommodation and conducive learning environment for better performance of students.