The study is aimed at knowing the most typical errors of grammar done by the second grade students of SMP Negeri 282 Jakarta Utara. The writer administered a guided test on writing. Moreover, to differentiate between errors and mistakes, the writer asked the student to do the same test on the different day. First, the writer showed the mistakes done by the students by underlining them. Then from the second writing the writer got the students errors. After getting the data, the writer analyzed the errors and categoried based on the grammatical aspects. The study shows that the most typical error done by the second grade students of SMP Negeri 282 Jakarta Utara is in capitalization which takes the first place with 38.27 %. The writer found that the students made this error because they are still confused at Indonesian language and English. Also the habit of their mother language influenced them in learning second or foreign language. Then, the second errors are singular-plural and word choice with percentage of 11.06 %. The third is run-on sentence with 9.51 %. It can be seen that the errors are mostly made because of the lack of practicing and knowledge in learning. It means the context of learning and interlingual transfer are the most typical source of errors.