This study explores the effect of graphic organizers (concept maps and KWL charts) on Omani EFL students' reading comprehension of expository English texts and their attitudes towards using these tools. This study is quasi-experimental. The target population of this study is all grade 11 students, makes and females, in Al Sharqiah North governorate of Oman who enrolled in this grade in the academic year 2015-2016. Four classes, two male classes and two female classes represented the experimental groups. The first experimental group was taught expository texts using concept mapping only, whereas the second experimental group was taught reading using KWL Charting along with concept mapping. The other two classes, one male and one female, acted as control groups and were taught following the teacher's book instructions, conventional method. This study addressed the following questions: 1. Does students' performance in reading comprehension vary according to the teaching method (KWL charting together with concept mapping, concept mapping only and the conventional instruction)? 2. Does students' performance in reading comprehension vary according to their gender across strategies? 3. Is there any significant difference between the students who use concept maps only and those who use a combination of KWL charts and concept maps in their attitudes towards using graphic organizers in reading comprehension classes? The researcher collected the data using two instruments to answer the aforementioned research questions & reading comprehension and an attitude questionnaire was developed to explore the students' attitudes towards the use of grophic organizers in their reading comprehension classes. The findings of the reading comprehension test showed a statically significant difference between the three groups in favor of the second experimental group as analyzed using one-way ANOVA. This result indicates the addition of KWL chart to the concept map was effective. Moreover, no significant difference was found between the first experimental group and the control group. Regarding the gender difference in reading comprehension performance, applying the independent samples t-test showed that female students outperformed male students in the control group, However, a significant difference in favor of males was found in the first experimental group, whereas no significant difference between genders was revealed in the second experimental group. The results of the questionnaire about the students' attitudes towards the use of graphic organizers in their reading comprehension classes showed no significant difference between the experimental groups, and the opinions were positive. Recommendations for further research and for improving the current educational practices are suggested in light of the aforementioned findings.