The aim of this study was to understand adult learners' strategy use in foreign language learning. It also explored how such strategy use relates to learners' sense of self-efficacy, self-regulated learning, and language proficiency. Two questionnaires were administered to obtain data from 90 education majors in a Japanese university. Differences in strategy use in relation to self-efficacy, self-regulatedness, and proficiency were examined using Kruskal-Wallis H tests. Whilst some preferred and less preferred strategy items were identified, the findings suggested that possession of a high self-efficacy profile and self-regulatedness related to both greater use of language learning strategies and a higher level of language proficiency. However, a closer look detected a nuanced, important difference in the magnitude of the effect, whereby self-regulatedness may be more yielding than self-efficacy. Namely, self-regulatedness played a substantial role in differentiating use of several strategy items among different proficiency groups, whereas self-efficacy seems to play a smaller part than self-regulatedness in this respect, considering the effect sizes. Thus, this empirical study contributes to the ongoing discussion of the different roles and nature of the self-efficacy and self-regulatedness constructs in the context of language learning and teaching. Implications for language teaching are discussed, and directions for future research are suggested.