The aim of this study is to investigate the effect of using Computer Assisted Grammar Instruction program on 6th grade grammar performance. It focuses on answering the following questions: Is Computer Assisted Language Learning (CALL) more effective than face to face class instruction in grammar teaching to grade six students in the basic education schools in Oman from the achievement test perspective? Is Computer Assisted Language Leaming (CALL) more effective than face to face class instruction in grammar teaching to grade six students in the basic education schools in Oman from the students' perspective as mirrored in the attitude questionnaire? The study consisted of the sixth grade female learners in an Omani government basic education school in the academic year 2008/2009. They were 56 female learners in the basic sixth grade in Al-Dhahira Region, divided into two groups. The first group, the experimental group was made up of 28 learners who used Computer Assisted Grammar Instruction program. The second group comprised of 28 learners who were taught grammar using the traditional method inside the classroom. To answer the research questions, two types of instruments were used. First, an achievement test was used to measure leamers' grammar achievement following the completion of the experiment. Second, a questionnaire was used to asses learners' attitudes towards using Computer Assisted Grammar Instruction programs. The major findings of the present study were s follow: • There was a statistically significant difference between the achievement of the control group and the achievement of the experimental group in favour of the experimental group, which used the Computer Assisted Grammar Instruction program. As for the results of the results from the attitude questionnaire that was dministered to the experimental group only to measure their attitude towards using Computer Assisted Grammar Instruction programs, it was clear the experimental group had positive attitude towards using the Computer Assisted Grammar Instruction program. In the light of these results of this research a number of recommendations were made.