This study investigates the concept images of ”any two vectors with same dimensions have an inner product” for senior high school students. A questionnaire survey was utilized to collect qualitative and quantitative data. A purposive sampling was used to sample 149 12th grader s in four classes from a high or a middle level school with either science or liberal-arts oriented approach. The findings included that more than 40% students did not possess the concept images of having an inner product for vectors with different starting points; only about 40%students' concept images were stable that did not switch over different vector relations; and students' concept images in question were influenced by the related concept images of vectors, angles, and definition of inner products.