Abstract: Students in the process of learning language profit from the errors they produce by making new attempts to successively achieve their desired objective. However, if these errors were not analyzed, detected and, consequently corrected by proper feedback from students’ lecturers, these errors will continue to grow as the process of learning English continue. In the current study, it is assumed that Arab school students face major difficulties in writing passive voice and subject-verb agreement due to intralingual reasons. However, the students’ language proficiency level was also considered as a possible factor. Therefore, the aim of the current study was to identify the types, frequencies and possible reasons of making errors in writing passive voice and subject-verb agreement by Arab EFL learners. The frequency tests using Microsoft Excel showed that the students face major difficulties in the two areas of writing as they produced a relatively huge number of errors. Five types of errors were identified misinformation, replacement, omission, addition and wrong formation with the misinformation the most frequent in writing passive and omission in writing subject-verb agreement. The proficiency level of students was found very effective as the students with lower proficiency produced noticeably more errors than the higher level students. The study recommended that future research consider other grades of school students, the gender of student and other areas of writing.