Abstract This study investigated the effectiveness of specialized monolingual and bilingual supplementary corpora in translating various texts by advanced-level students in Iranian English Language institutes. It aimed to determine whether providing students with on-line supplementary corpora might have any effect on Iranian EFL learners’ translation ability. To answer the question, 60 advanced-level language learners from several language institutes in Tonekabon and nearby cities participated in the study. The subjects were randomly assigned to two groups (experimental and control, 30 in each group). The purpose was to observe any probable progress with regard to the translation ability (TA) of the students from the beginning toward the end of the program. The subjects took a standard OPT test to demonstrate their English proficiency. A translation pre-test from English to Persian was administered while all the subjects were asked to use handy dictionaries to indicate their translation ability in each group. After 10 sessions of treatment a post-test of translation was administered. The experimental group translated a text by using any bilingual and monolingual handy dictionaries as well as on-line corpora as the supplement while the control group translated the same text just by using handy dictionaries. The data were analyzed using Independent sample t-test. The results showed that the quality of translation was improved as a result of using corpus-based translation tools. Keywords: Corpora, Corpus-based translation, supplementary corpora, Translation Ability