Previous research has shown that second language (L2) learners can learn new words incidentally through contextual clues. However, little is known about whether derivational affixes can be learned in a similar manner. Addressing this gap, the current study examined whether English as a Foreign Language (EFL) learners could acquire knowledge of English derivational noun suffixes through contextualized reading. Forty Chinese EFL learners participated in the study, completing offline pre-tests and post-tests to assess improvements in three aspects of suffix knowledge. Participants’ eye movements during reading were also recorded to investigate the relationships between online processing of derived words and suffix learning. The offline test results showed that the learners made significant progress in three aspects of suffix knowledge. Multilevel logistic regression analyses further indicated that improvements in accuracy were significantly predicted by eye fixation measures, learners’ L2 proficiency, and language-level factors. Findings indicate that incidental learning while reading can effectively supplement intentional learning, particularly for English affixes that occur less frequently.