SUMMARY
Looking up unfamiliar words and writing their meanings in the margin of the texts is a common lexical processing strategy which serves to comprehension and retention of words’ meanings when reading English academic textbooks. This study investigated words in academic textbooks looked up by Iranian university TEFL students in hopes of throwing light on challenges and errors they experience. The findings revealed that students extensively consulted the dictionary and were successful in many cases but their dependency on bilingual dictionaries and also their tendency to rely on the initial sense provided in the dictionary led to failure for cases such as technical terms, polysemous entries, and words with different parts of speech. Among the pedagogical implications of these findings is the need for further training of students for effective use of the dictionary while reading academic texts.