The purposes of this research were to: 1) investigate the strategies used most frequently and those perceived as most useful by proficient and less proficient learners, and 2) analyze how the learners’ frequency of strategy use related to their perceptions of the strategy usefulness. The sample consisted of 70 Thai EFL undergraduates at Thammasat University who were selected by a purposive sampling method. They were divided into two groups: 35 proficient English learners and 35 less proficient English learners. The research instrument was vocabulary learning strategy questionnaire. The data were analyzed by using means, standard deviations, and Person product-moment correlation coefficients. The results were as follows: 1) the proficient English learners employed a more variety of strategies and had a higher frequency of use than did the less proficient English learners, and 2) the learners’ frequency of strategy use was found to strongly correlate with their perceptions about the usefulness of strategies at the .05 level of statistical significance.