Background : The complexity of planning and implementation of OSCE (Objective Structured Clinical Examination) activity may influence the quality and reliability of OSCE as a tool to assess the clinical performance. Many factors can make OSCE assesment becomes less realible. A good OSCE activity plan is an important factor in supporting the reliability of OSCE. The purpose of this study was to describe five essential keys in OSCE planning from many resources and researches. Discussion: The implementation of OSCE needs good structured steps. There are five essential keys in OSCE planning, those are OSCE design, standardiced patient, examiner, infrastucture, and standard setting. OSCE design includes composing blue print of OSCE, composing case stations and rating scale form. Composing blue print is the first step in designing the OSCE. Blue print is composed to ensures that various individual competencies will be examined several times in some station and each station contributes to complete the exam by assessing some kind of compencies. Conclussion : Preparation some kind of essential keys in OSCE planning has to be done in a stuctured plan by the exam committee in order the assessment becomes objective, valid, reliable, and resulting trusted information.