The problem of the study was defined as knowing the commongrammatical mistakes in the written production of the secondary students in thesultanate of Oman.The study aimed to answer the following questions 1-What are the common grammatical mistakes in the written production on the secondary students in the Sultanate of Oman? 2-Does the type of mistakes differs according to the different classes in which the student? 3-Does the type of mistakes differs according to the specialization (Arts of science ) of the student? 4-Does the type of mistakes differs according to the sex (male, on female of the students? 5-What are the reasons behind these mistakes from the point view of the Arabic teachers and inspectors? 6-What is the remedy plan to eradicate these mistakes? The sample of this study consisted of (317) male and female students from Al-Batinah (north) region, 6 Arabic inspectors and 20 Arabic teachersTo answer the question the study used the description method and depended of several statistical techniques such as frequencies and percentagesThe study used three main methods for data collection First, the study contained a questionnaire to determine the Arabic teachers opinions about the grammatical topics that should be taught to secondary dents. The second method was the analysis of the grammatical mistakes committed by the secondary students. The last method was a questionnaire for theArabic inspectors. The purpose of the questionnaire was to get their opinions about the reasons behind the mistakes and their suggestions to eradicate them. The study reached several conclusions. The most general findings were that there are five grammatical topics in which the students made the highest mistakes. In addition to that, the female students were better than the male students with regard to certain grammatical topics. Furthermore, the science students showed remarkable ability in using or applying the grammatical rules than the Arts students. The study recommended that the areas that showed the highest mistakes should be given more attention in the grammatical exercise book. It also necessitated on training the students on talking in correct Arabic Language Moreover, it recommended that the grammar should be related to the other aspects of the Arabic Language.The suggestions of the study centered around knowing the common grammatical mistakes in the oral production of the secondary students. The secound suggestion was to formulate a remedy programme to eradicate the common mistakes ( written & oral) of the secondary and preparatory students