The purpose of the present study was to identify any significant relationship between critical thinking ability, L2 vocabulary knowledge, and L2 vocabulary learning strategies of Iranian EFL learners. To this aim, the productive vocabulary levels test was administered to measure the learner’s L2 vocabulary knowledge and observe homogeneity in terms of vocabulary knowledge. At the second stage, a critical thinking questionnaire was administered, along with a newly-developed L2 vocabulary learning strategies questionnaire; the questionnaires were developed to specify the critical thinking ability and L2 vocabulary learning strategies of the individual participants. The results of the statistical analysis revealed that Iranian EFL learners’ L2 vocabulary knowledge was significantly related to their critical thinking ability. The participants’ critical thinking ability also correlated positively with their self-assessed degree of determination, memorization, cognitive, and meta-cognitive strategies of L2 vocabulary learning. The study also showed a positive relationship between participants’ L2 vocabulary knowledge and their L2 vocabulary learning strategies.