This paper introduces a corpus-driven measure as a method to assess EFL learners' knowledge of semantic prosody. Semantic prosody here is defined as the tendency of some words to occur in a certain semantic environment. For example, the verb "cause" is associated with unpleasant things--death, problem and the like. Subjects were 60 Iranian Persian-speaking English learners drawn from 180 candidates taking English classes in five language institutes. To estimate the quality of the test, a 70-item test of semantic prosody was constructed, validated, and used to measure the subjects' knowledge of semantic prosody. The items were selected from COBUILD Dictionary and were mainly based on those cases of semantic prosody whose conditions (positive or negative) had been already determined by researchers. A proficiency test was applied to determine learners' level of language proficiency as a variable which may affect the results. Data analysis showed that learners' knowledge of semantic prosody is, and can be, appropriately measured by the corpus-driven test of semantic prosody. The implications of the findings for teachers, learners, and test developers are discussed.