Abstract: The present study was intended to investigate the effectiveness of CALL on Iranian EFL learners' vocabulary learning in two institutes in Tehran, Iran, as compared to those students receiving traditional instruction using the printed text materials. CALL (Computer Assisted Language Learning) has given man versatility in many areas, and seems the paramount representation of technology for today. The goal of the study was to examine the effects of the application of CALL on students،attitudes towards CALL before and after the instruction. To carry out the study, 60 homogeneous male and female participants were selected from among students and randomly assigned into two groups, the traditional group and CALL group. A vocabulary achievement test as pre-test was administered to participants of both groups. The results of t-test confirmed that there is no significant difference between the participants regarding their vocabulary knowledge. The Computer Assisted Instruction group experienced 16 sessions of instruction using the CALL. The traditional instruction group received the same hours of instruction and materials but on paper with no audio-visual features. The result of paired sample t-test between pre-test and post-test of both groups of study revealed that there is a significant difference between experimental and control group regarding their vocabulary knowledge. CALL instruction improved EFL learners' knowledge of vocabulary. Besides, the results of descriptive statistics showed that the group who received Computer Assisted Language Learning was outperformed in this study.