The purpose of this study was to investigate errors on written tests of science, matters, in middle school 7th grade. Errors were defined something you have done which is considered to be incorrect or wrong, or which should not have been done. We found and classified errors, and then examined the frequency of types of errors on the written tests. A total of 167 test items from 10 middle schools were analyzed for this study. Errors on the written tests were classified into 5 types: insufficient information; unnecessary information; inaccurate information; information against curriculum; and unclear information. A total of 81 errors were counted out of 167 test items. The results of this study are expected to help teachers develop written test items to convey definite meanings by text and would be used as basic information for improving written test item standards.