The present study is descriptive and analytic in nature. Its population was basic education students in grades four and ten in the academic year 2012-2013 in the Sultanate of Oman. Its sample consisted of 260 grade four students and 376 grade ten students and was extracted from basic education schools in Al Batinah South Governorate. The current study aimed at investigating the gender gap in English as a foreign language (EFL) reading achievement of male and female basic education students in grades four and ten. It also aimed at investigating the relationship between these students' reading achievement and their perceived reading self efficacy beliefs. In its analytic nature, the study analyzes the differences in these beliefs in light of gender and grade level and the interaction between the two. Therefore, the study addressed the following research questions: 1. Are there any significant differences in reading achievement between male and female students in grade four basic education? 2. Are there any significant differences in reading achievement between male and female students in grade ten basic education? 3. Are there any significant differences in reading self-efficacy beliefs between male and female students in grade four basic education? 4. Are there any significant differences in reading self-efficacy beliefs between male and female students in grade ten basic education? 5. Are there any significant differences between the reading self-efficacy beliefs of male and female students in grades ten and four basic education? 6. Is there a relationship between male and female students' reading self-efficacy beliefs and their reading achievement in each grade level? Two instruments were used to collect the data to answer the research questions: national reading achievement tests obtained from the Ministry of Education and a reading self-efficacy beliefs scale developed by the researcher. The collected data was analyzed using the SPSS program. Specifically, the independent sample t-test was used to find out the differences between the genders and the Pearson Product- Moment Correlation was used to investigate the existence of a relationship between self-efficacy beliefs and reading achievement. Findings revealed that there were gender gaps in the EFL reading achievement in favor of females in both grades four and ten. Moreover, the findings showed that females in both grades held a higher level of reading self-efficacy beliefs for their EFL reading achievement than males did. Added to that, the findings showed that grade four students reading self-efficacy beliefs for EFL reading achievement was higher than these of grade ten. Finally, the findings showed a positive relationship between reading self-efficacy beliefs and the reading achievement of students in both grades; students with a higher level of self-efficacy beliefs for EFL reading achievement tend to perform better in reading. In the light of these findings, the researcher suggested that more attention should be given to the instruction of EFL reading for boys. Moreover, intensive research and studies should be conducted to find out the causes of the low achievement of males compared to females as a step towards finding solutions to this phenomenon. In addition, efforts should be exerted to facilitate the development of EFL reading self-efficacy beliefs. This can be achieved by facilitating reading tasks by which learners can reach the planned goals, encouraging learning from peer observation experiences, providing positive verbal reinforcement, and creating positive emotional arousal atmosphere in the EFL reading classes.