The purpose of the present study was twofold. Firstly, it tried to investigate the relationship between the technical English proficiency of the students of Mechanical Engineering in the universities of Iran and their technical translation proficiency in translating technical texts of Mechanics. Secondly, it attempted to evaluate the effectiveness of one of the ESP courses being taught to the engineering students in improving their ability to translate texts of their own field from English to Persian. For the first purpose, two sets of tests were administered to 50 male and female students: a technical multiple-choice translation test and a technical English reading comprehension test. For the second purpose, the first test used above was administered two times with a two-month interval. Analyzing the data using SPSS indicated that there is a moderate significant correlation between technical English proficiency and technical translation proficiency; and that the ESP course under investigation is approximately sixty percent effective in enhancing the learners' proficiency in technical translation.