This study explored the relationship between text authenticity and test takers’ performance on C-Tests. To fulfill the objective a single C-test was developed on an authentic text (AC-test) and along with standard C-Tests (Klein-Braley 1997) and a disclosed Test of English as a foreign language (TOEFL) was administered to one hundred thirty five junior and senior undergraduate university students majoring in English language and literature, English translation and teaching English as a foreign language in two universities in Iran. Similar to their standard counterparts, the AC-test correlated significantly not only with the TOEFL but also with its structure, written expression, vocabulary and reading comprehension subtests and thus established itself as an externally valid measure of English language proficiency. Although the significant and high correlation coefficient obtained between the authentic and standard C-Tests (r = 0.87, p <.01) showed that they could be used interchangeably, the AC-Test enjoyed slightly higher internal validity and noticeably higher reliability. The implications of the findings are discussed within a foreign language context.

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