This study was developed to provide a possible solution to the problems and difficulties encountered by the office of student affairs in a secondary high school in the Province of Nueva Ecija, Philippines. It covers the management and organization of student records and the effective delivery of information through Short Message Service (SMS) notification to students, parents, and guardians. This study utilized a developmental method of research and clustered-random sampling composed of Information Technology (IT) professionals, secondary high school students, and teachers. The system was developed following the phases of Software Development Life Cycle (SDLC) which include Planning, Analysis, Design and Coding, Testing, Implementation and Maintenance. A series of observations and interviews were done to identify the needed requirements. The results of data gathering procedures were the basis for the development of the system. The system was developed using Microsoft Visual Studio environment and MS VB.NET as the programming language. The database was constructed using MySQLYog environment and Structured Query Language (SQL). The developed system was assessed on the basis of its technical quality and quality of use. The technical quality was based on the International Organization for Standardization (ISO) 9126 standards which includes Functionality, Reliability, Usability, Efficiency, Maintainability, and Portability while the quality of use was assessed based on three criteria which include relevance, feedback, and graphical user interface. The Online Student Affairs (OSAS) with Short Message Service (SMS) passed the assessment made, and was proven to be beneficial to the Office of the Students Affairs of a Secondary National High School.