Applying technologies has recently caused language education to undertake influential modifications. Hence, this study tried to investigate the impact of using technology in form of multimedia on improving grammar knowledge of Iranian high school students and also examined their attitudes toward multimedia-based mode of instruction. To do so, three intact classes of lower intermediate students were randomly divided into three groups: multimedia, multimedia + textbook, and control group. After homogenizing the groups regarding their proficiency level, the pre-test was run and results indicated no significant difference. Treatment lasted for 8 sessions, during which the first experimental group was taught through using multimedia elements like cartoons, texts, and Power Point Presentation. The second group had their textbook besides multimedia, while the control group was instructed traditionally by means of the textbook. Comparing the groups’ scores on the post-test revealed the superiority of multimedia + textbook group over the other groups in their grammar test performance. The questionnaire outcomes also showed more positive tendency of the students in this group in comparison to the multimedia only group toward application of multimedia programs. Findings of this study might open a novel way to assist EFL learners to increase their grammar knowledge more successfully.