: The purpose of this research is to describes: (1) the error model of Indonesian language that includes errors in spelling, diction, sentence, and paragraph; (2) causes of error in the observation report of SMP Negeri 8 Surakarta grade eight students; and (3) the effort which is done to solve the errors. This research is a qualitative descriptive research with a sample observation report of the SMP Negeri 8 Surakarta grade eight students. The results of this research are as follows. Firstly, the error of Indonesian language found in the observation report of SMP Negeri 8 Surakarta grade eight students includes: errors in spelling are 163; errors in diction; errors in sentence ; and errors in paragraph. Secondly, the factors of error in the observation report of SMP Negeri 8 Surakarta grade eight students causes by four factors, among other: mastery of spelling USAge less than adequate; inacuracy in writing; lack of writing motivation; lack of vocabulary. Thirdly, the efforts have been made to minimize the errors include: implementing a process approach to teach writing, improving students' language mastery; having more practice in writing.