Background. Nowadays, almost all indexed journals expect submissions in English, which is a great challenge for exophonic authors. Code-switching context, where cross-language effects, especially native language interference, are well distinct, is critical for approaching the dilemma. Navigating the complicated issues of language-related challenges will be impossible without referring to three crucial levels of written production: lexical, syntactic, and textual. In our investigation, we address the nature of potential errors and their inter- and intralingual origins. In particular, we identify and interpret the deviations from Standard English in scholarly research writing of Ukrainian authors in the field of life sciences, exemplify and classify errors into categories based on the type of language misuse. Materials and Methods. Language material for the study comprised 50 manuscripts submitted by authors from Ukraine to the journal “Studia Biologica”. This research is a mixed-method study encompassing descriptive qualitative and descriptive quantitative methods. Content analysis was employed as the data gathering technique. The analysis of texts was focused on tracing deviations from consistent principles and rules of Standard English and linguistic features of English research discourse and encompassed such steps as highlighting the error, cross-checking and stating the deviation, listing and classifying the errors, and tracing a possible connection of the error to authors’ first language interference. Results. The study identified language areas where Ukrainian authors fail to effectively communicate their ideas to the global academic community. At the textual level, the problem areas encompass defective paragraph structure and excessive verbosity. At the syntactic level, the most critical deviations from the language and stylistic norm comprised misuses of word order and clauses, wordy and confusing sentences with multiple issues that hinder the readability of text. The most widespread grammatical mistakes include missing predicates, faulty subject-verb agreement, incorrect forms of the verb, and inappropriate use of articles, pronouns, demonstratives and quantifiers. At the lexical level, the prevalent errors relate to various types of loan translation, but also include improper word choices and poor vocabulary. Orthographic mistakes, though in minority, refer to the spelling of toponyms, capitalisation, switching from American to British orthographic standards and other random spelling errors. Conclusions. An insight into the nature of the analysed deviations suggests the presence of both intra- and interlingual factors that cause mistakes in papers submitted for publication in the field of life sciences. The error analysis can be beneficial in the educational process for both educators and practitioners. Proper understanding of the functional mechanism of the mistakes might increase the awareness of the potential pitfalls and consequently help avoid them. The classification of errors can be adopted in the educational process and contribute to the development of error pedagogy.