Concordancing in the classroom is fairly a new approach which has emerged with the use of corpora in language learning. In a concordance, language is presented in natural setting; learners are able to examine a key word in the context of a string of sentences which can exemplify the use of that particular word. Learners need not rely heavily on their teachers or their own intuition as they can explore specific language features from the vast amount of information in the corpora. Vocabulary knowledge acquired from a concordance can be transferred to novel texts (Cobb, 1999) to enhance student writing. This study examined if the use of an on-line concordance program together with an on-line dictionary by ESL undergraduates helped them acquire receptive word knowledge and if that word knowledge was transferred correctly to an academic writing task. The treatment and control groups did not refer to any tools during the pre- and posttest. However, when completing vocabulary activities, they had access to an on-line dictionary but only the treatment group had the opportunity of using an on-line concordance program. A comparison of pretest and posttest scores showed that the performance of the treatment group remained constant. The results indicate that while there was no acquisition of receptive word knowledge in the treatment group, there was transfer of vocabulary knowledge to the writing task. The results also showed a fairly strong correlation between participants' look-up behavior with the concordance program and the percentage of correct words in the posttest. However, it was inconclusive if the use of concordance affected productive word knowledge.