Technological developments and their utilities in various areas including education have offered great advantages for man. One of the greatest achievements in this trend has been the innovation in computer software like Lexical Frequency Profiles (LFP) and its pedagogical implications either in teaching or measurement. To take the maximum advantages, this study seeks to validate the LFP as a measure of lexical richness in written discourse of Iranian EFL Learners. 50 students majoring in English Translation participated in this study; each of them was encouraged to develop two compositions on general topics in order to establish VocabProfile indexes. To estimate the reliability of the LFP, the VocabProfile indexes of two writings were correlated, but for the validity purpose, first, a productive version of Vocabulary Levels Test (VLT) was administered and second, the students’ compositions were fed into P_Lex software to elicit P_Lex index. After that, VocabProfile indexes were correlated with VLT scores and P_Lex index separately. The findings of the study revealed that students’ VocabProfile indexes written on two different topics correlated significantly with each other. Because of such a significant correlation coefficients, and the LFP indexes are related to VLT active test and P_Lex index, it is conservatively safe to claim that VocabProfile indexes are to some extent reliable and valid measurement instruments but not strong enough to be used as a stand- alone measure for the assessment of lexical richness. Pedagogically speaking, the LPF is suggested as a relatively reliable and valid measure to be used along with other dependable devices in measuring lexical richness in discourses of various types.