This study aims to tackle an answer to the main question; if there is a relationship between the vocabulary size of adult English language learners and their morphological awareness and if their performance would differ in word complexity. The participants were 90 senior BA English Language and Literature students from Jordanian universities. The two empirical research tools were the Vocabulary Size Test and Morphological Awareness Test. The results revealed the mid-frequent level vocabulary size of the participants, and they were unable to form and use new words using morphemes. A positive correlation between the vocabulary size of the participants and their morphological awareness existed. Besides, a positive relationship existed between their performance on word complexity and their morphological knowledge. Pedagogical solutions need to be implanted in "English as a Second Language (ESL)/English as a Foreign Language (EFL)" classes.