Since vocabulary acquisition is essential in L2 processing, its especially necessary to probe into efficient vocabulary learning strategies.The present study is conducted to verify the hypothesis that the knowledge of English derivational affixes is helpful to promote the acquisition of vocabulary, which is based on a teaching experiment in which two groups of participants are required to memorize new English words.The statistics results of two tests (cued recall and recognition) show that the experimental group (with the help of derivational affixes) significantly outperformed the control group (by rote learning) (p<0.001).Based on the results, the vital importance and some using deviation (such as overuse, confusion and spelling errors) of English derivational affixes in memorizing vocabulary are discussed.The findings of the study also shed some light on pedagogic implications in L2 vocabulary teaching.