The present study attempts to explore the effect of language proficiency on the ability to guess the grammatical roles of unknown words, to make use of contextual clues, and to guess the meaning of unknown words from context by examining EFL learners majoring in different departments at university. Guessing from Context Test (GCT) developed by Sasao and Webb (2018) was used to collect data to measure EFL learners' guessing skills as well as their ability to identify both the part of speech of an unfamiliar word and contextual clues that help them infer the meaning of unfamiliar words. The findings indicate that English-major EFL learners significantly perform better than non-English major EFL learners in each of the three categories in the GCT. More specifically, correctly guessing the meaning of unknown words lags behind correctly guessing the grammatical class of unknown words in both groups. Similarly, the rate of correct guessing of contextual clues in both groups is not as high as the grammatical class of unknown words. On the other hand, while English-major EFL learners correctly guess the meanings of the words for which they cannot correctly guess the clues, non-English major EFL learners cannot benefit from correctly guessed contextual clues to guess the meaning of unfamiliar words. Also, nouns and verbs are the word groups whose grammatical class is best predicted in both groups.