Vocabulary learning strategy plays an important role in vocabulary acquisition; one of the major vocabulary strategies is word part strategy. The purpose of this study is to investigate whether word part strategy can help students to understand words and facilitate vocabulary acquisition. Ten teacher trainee students from a university in Sweden participated in the study. All were given a vocabulary pre-test, a lecture about word-formation rules, two vocabulary tests and a questionnaire. The results show that word part strategy is helpful in understanding words and facilitating vocabulary acquisition. The strategy is especially useful for those students who have a good knowledge of affixes. In addition, the choice of affixes also affects the application of word part strategy. In order to master word part strategy, more time is needed to learn the meaning of affixes and to practise how to re-express the meaning of words with the aid of the meaning of the word parts. The results of the study show that there are great differences between individual results, which, in turn, leads to a questioning of the efficiency of word part strategy. The present study is a starting point for further research on the connection between students’ level of English and the effectiveness of word part strategy as a teaching method.