This exploratory study investigates Korean non--native English speakers’ comprehension of plain English and recommends plain English guidelines that consider Korean non--native English speakers who are in the United States studying at university. This study has two parts. First, this paper explores how Korean speakers understand Latinate and phrasal verbs with a matching test and interview. The results demonstrate that Korean speakers generally prefer Latinate verbs. Second, this paper investigates whether or not plain English that works best for native English speakers also works best for Korean non--native English speakers. This study includes a usability test that evaluates Korean speakers’ comprehension of six passages written in plain and non--plain English, excerpted from a variety of topics. The results indicate that using plain English help Korean speakers’ comprehension of English in general, however; it does not always guarantee Korean speakers’ better comprehension of English. Also, it implies that concise sentences could occasionally make Korean speakers less assured of their comprehension. This study recommends that technical communicators use Latinate verbs instead of phrasal verbs and they conduct usability tests of their writing, in that way they can make revisions as necessary, if their target audience includes Korean non--native English speakers.