The study was conducted on impact of students' teacher relationship on post-primary schools' administrative effectiveness in Ondo State, Nigeria. The population of the study comprised, teachers and students at secondary schools. The sample size of the study was One hundred and thirty (130) respondents were selected, through a simple sampling technique . Three research questions were raised.Data were collected through, a self-structured questionnaire by the researcher, titled, "Questionnaire on Impact of Student- Teacher Relationship on Post- Primary Schools' Administrative Effectiveness in Ondo State, Nigeria", fashioned on four likert rating scale;Strongly Agreed (SA), Agreed (A), Disagreed(D) and Strongly Disagreed( SD ,rated on 4,3,2 ,and 1 points). The research instruments were validated by three experts in Measurement and Evaluation .Its reliability wa sdetermined, through test-retest method at two weeks interval, 0.69 coefficient reliability was established. Data collected were analyzed, using descriptive statistics (frequency counts and simple percentage. Based on the results of the study, conclusions were made that student-teacher relationship could result into effective students' academic planning, achievement of school goals, improved students' academic performance, positive schools' climate, students' adherence to rule and regulation of the school and social-peace stability in the school. Therefore, recommendations were made that; teachers should establish a good relationship with their students; school managers should be educated on how to promote positive student-teacher relationship; students and teachers alike should be educated and enlightened on the benefits of students-teacher relationship to effective administration , and so on.