The goals of this research are: (1) To identify the grammatical errors made by the students in writing descriptive text;(2) To know the percentages of grammatical error made by students in writing descriptive text;(3) To know the most difficult aspect of grammatical error for students in writing descriptive text; and (4) To identify the sources of grammatical errors made by the students in writing descriptive text. The research was conducted in SMK Pancasila Surakarta in June 2017. The method of this research is descriptive quantitative research. The sampling technique employed in this research is cluster random sampling. The data are student’s errors which are collected through test which is done by 26 students of X TPM 1 of SMK Pancasila Surakarta. The data are analyzed by using error analysis procedure which consists of identifying students’ errors, describing the errors, explaining the errors, and evaluating the errors. The findings of the research are: (1) The grammatical errors made by the student are classified into four classifications: omission, addition, misinformation, and misordering;(2) The percentage of each error is as follows: omission of error with the percentage of 33.34% or 38 errors of total 114 errors, addition of error with the percentage 10.53% or 12 error of total 144 errors, misinformation of error with the percentage of 54.38% or 62 errors of total 114 errors, and misordering with the percentage of 1.75% or 2 errors of total 144 errors;(3) The most difficult aspect is errors of misinformation which are the most frequent error that are identified by the use of incorrect form of morpheme or structure; and(4) The sources of error made by the students are divided into two types; interlingual error with the percentage of 45.62% or 52 errors of total 114 errors and intralingual error with the percentage of 54.38% or 62 errors of total 114 errors. The study can be used by the teachers to know what kinds of errors which are often made by the students. The teachers can determine the best teaching method and technique to deliver the lesson in order to avoid the occurrence of errors. Besides, teachers can also find out what materials should be prioritized to reduce the students’ errors.