The study was conducted to examine quality assurance indicators as predictor of principals’ administrative effectiveness in secondary schools in Abia State, Nigeria. Specifically, the study investigated the contribution of school leadership and instructional supervision to principals’ administrative effectiveness. Two null hypotheses were formulated to guide the study. The design adopted for the study was correlational research design. The population comprised 244 public secondary schools and 244 principals in Abia State covering three education zones in Abia State namely; Aba, Ohafia and Umuahia. Census technique was used to select all the 244 secondary school administrators for the study. The instrument used for data collection was a questionnaire designed and administered by the researcher tagged: “Quality Assurance Indicators and Principals’ Administrative Effectiveness Questionnaire (QAIPAEQ).” The validity of the instrument was confirmed by three experts from the Department of Educational Management and the Department of Educational Foundations (Measurement and Evaluation Unit) University of Calabar. The reliability of the instrument was determined using the Cronbach alpha method, yielding coefficient values of 0.81 and 0.87, respectively. The null hypotheses were tested at .05 level of significance using Simple Linear Regression analysis. Findings of the study revealed that school leadership and instructional supervision significantly predicts secondary schools’ effectiveness in Abia State. Based on the findings of this study, it was concluded that quality assurance indicators significantly predict principals’ administrative effectiveness in Abia State, Nigeria. The study concluded that school leadership and instructional supervision are significant predictors of principals' administrative effectiveness. This means that effective school leadership which is characterized by clear vision, strong decision-making, and collaborative practices, combined with consistent instructional supervision, substantially enhances the ability of principals to manage school operations efficiently, support teachers, and improve student outcomes. Based on the findings, it was recommended that: Ongoing professional development programs should be provided for school leaders, focusing on instructional leadership, effective communication, and change management. This will enhance their capacity to foster a conducive learning environment and drive continuous school improvement.