Misconceptions can affect the student's mindset, resulting in a misconception. The purpose of this study was to determine the level of misconception experienced by students on the material of motion straight with a twotier diagnostic test instrument. A total of 15 diagnostic test questions were tested to 26 selected students with the consideration of having studied straight-motion materials. This research is a qualitative descriptive study. Based on data analysis and discussion shows that the student misconception level on the material of straight motion is moderate. This is based on the percentage of students who experienced misconception of 44,61%, while students who understand the concept of 35,38% and the percentage of students who do not understand the concept of 20%. The highest average misconception is the sub-subject of free fall motion on indicators identifying and distinguishing between objects of different mass dropped together; sub-subject of irregular straight motion on indicators identifying and distinguishes between velocity and speed; as well as sub-subjects of upward vertical motion on indicators identifying and distinguishing between velocity and acceleration of objects when reaching maximum height.