The study aims to explore the grammatical errors in spoken English of Thai University learners in a communicative business English course. The main objectives of the research study are to identify the types and frequency of grammatical errors. Collected data were analyzed according to the surface structure taxonomy to present a general overview. The linguistic description approach on error was also used to present the findings in greater depth. The findings revealed that omission errors accounted for more than half of the total errors made by the sampled student population, followed by misinformation, addition and misordering. According to linguistic categorization of errors, the 3 most occurring errors were plural form, article, and verb form. Results yielded through error analysis will be valuable in the area of second language lesson and curriculum planning.