A foreign language for Indonesian students is English. Students sometimes do mistakes and errors in the process of learning English. The making of error cant be avoided in the learning process. Errors are the flawed side of learner speech or writing. They are those parts of conversation or composition that deviate from some selected norm of mature language performance (Dulay : 138). H douglas differentiate between error and mistake as follows: a mistake refers to a performance that is a random guess or a slip, it is a failure to utilize a known system correctly. Mistakes can be self-corrected than errors cannot be self-corrected because errors reflect the competence of the learners. So, mistakes are caused by students who cant memorize well, slip of tongue or slip of finger but errors are caused by lack of knowledge about target language.The errors that learners make are a major element in the feedback system of the process learning and teaching language (Corder:35). It shows the results of learning and teaching language. A teacher detects the errors through analyze what errors that students make.