A lower frequency of writing errors facilitates the process of knowledge transfer. In this study, we scrutinized the medical journals highlighting the most frequent and critical writing errors in published medical papers of Iranian English journals. As a sample, 25 published articles were randomly selected from recent issues of five Iranian medical English ISI journals (2019).  The frequency of discourse, lexical, grammatical, and mechanical errors was identified. In all five journals, more than 50% of errors are related to grammatical errors. The highest frequency of grammatical errors was in articles (79%), and the singular/plural errors had the lowest frequency in this category. Of Mechanical errors, the highest and the lowest errors were assigned to comma usage (25%) and spacing (5%), respectively. The discourse errors had the third position of error frequency among the journals (7.8%).   Also, the lexical portion was without error in these journals. Moreover, there is a statistically significant relationship between the impact factors of journals and Grammatical errors (P<0.001). Statistically, no significant relationship was observed between Mechanical errors and the impact factors of journals (P= 0.57). The highest error frequency among the main sections of articles (introduction, method, result, discussion) was in the discussion section (42.6%), and the lowest error frequency was in the result section (15%). These shortages arose from the difference between the grammars of two languages (native and target language) and the unfamiliarity of academic authors from these linguistic points. Adequate language proficiency and proper use of grammar could help the authors to transfer their knowledge efficiently. The findings of this study can help minimize some language-related difficulties in writing scientific papers in all fields of study. https://dorl.net/dor/20.1001.1.20088302.2021.19.2.12.0