This paper presents a study focusing on EFL learners' use of free online machine translation tools for their language studies. The study aims to explore how language learners perceive the use of the tools for this purpose, assess their comments on how frequently and extensively they think they use the tools, and examine how the tools are actually utilized. It also investigates whether proficiency level is a factor affecting the use of free online machine translation tools in second language learning. To this end, it was designed as convergent parallel mixed-methods research in which the data were collected through a questionnaire on the related issues and stimulated-recall interviews. The participants were 104 EFL learners with pre and upper-intermediate proficiency levels at tertiary level in T & uuml;rkiye. The findings suggested that the participants used the tools principally for vocabulary to check the meanings of English words, and they were aware of the extent to which their use could be considered as ethical. As for the potential effect of language proficiency, it emerged that there was no significant difference in the use of the tools by the two different language proficiency groups.