The purpose of this study was to improve Iranian EFL learners’ achievement and motivation using Successful Theory of Intelligence. The study used “quasi-experimental design. The study was conducted in Asan English institute in a city of Isfahan province, Iran. There were two groups, namely, control and experimental, from which the researcher selected 18 participants. In both control and experimental groups, participants were selected from low and high intermediate levels. A pre-test and a post-test were used in this study, both tests were selected based on the participants’ level in order to measure the efficiency of Successful Theory on learners’ reading skill and also sub skills including grammar and vocabulary. To measure the efficiency of this theory on learners’ writing skill, they were asked to write six writing assignments. The instruments for data collection for motivation and intelligence were two questionnaires: Gardner´s Attitudes/Motivation Test Battery (2004) and Successful Intelligence Inventory (SII) (2002). To analyze the data of questionnaires and tests, descriptive and inferential statistics were used. To test the research hypothesis, Covariance analysis (Ancova) was used.SPSS 22 was used for statistical analysis in this study. Finally, whole texts including fiction and nonfiction were analyzed through descriptive and inferential statistics. The results indicated that the difference between control and experimental group in terms of learners’ achievement scores at P 0/05 level was significant. Therefore, the Successful Theory of Intelligence improved learners’ reading skill, grammar and vocabulary sub skills. Likewise, different tests indicated a significant difference in terms of scores of learners’ fiction and nonfiction texts between two groups of experimental and control at P 0/05 level. Therefore, the Successful Theory of Intelligence improved learners’ writing skill. Results also showed a significant difference in scores of learners’ intelligence between two groups of experimental and control at P 0/05 level. As the data analysis suggested, the significant difference was found in both analytical and creative intelligence. Moreover, it was shown that there was a significant difference in intrinsic (self-confidence), and external encouragement. The difference between the two groups in intrinsic (integrative orientation), extrinsic (teacher and peer students) and integrative motivation, extrinsic (instrument), personal assessment and instrumental motivation was not significant. Keywords : Iranian EFL learners, achievement, motivation, analytical intelligence, creative intelligence, Successful Theory of intelligence