The purpose of the current study was to investigate the impact of the metacognition strategies (MS) in ninth grade students' science achievement, understanding of nature of science (NOS) and their attitudes towards science (ATS) in Oman for the academic year 2016/2017. A quasi-experimental design was used with two experimental groups and one control group. The first experimental group (n= 30) was taught via metacognition strategies based learning modules in paper form, while the second experimental group (n=34) was taught in computerized form, The control group (n=33) was taught in normal settings. The study continued for eight weeks at seven sessions per week. The Quantitative data of this study was collected by using an achievement test, a Likert scale of students' understanding of metacognition of nature of science ( MONOS) and a Likert scale of students' attitude towards science. The achievement test and the scale of students' attitude towards science contain (40) items, the (MONOS) scale contains (16) items. Their reliability were (0.84), (0.81) and (0.89) respectively. In addition, a qualitative data were collected by using focus group interviews for understanding of (NOS) by students in the experimental groups with (8) interviews per group. The results of the quantitative data showed that there was a significant difference between the means of the students in the three groups on the post- students' science achievement, in favor of the second experimental group. In addition, there was statistically significant differences between the means of the students in the three groups on both the post- students' understating of science (NOS) and on the post students' attitude towards science, in favor of the two experimental groups. However, there was no statistically significant differences between the means of the students in the experimental groups on both the post- students' understating of (NOS) and students' attitude towards science. Moreover, the effect of employing the MS on those students in their post students' achievement, students' understating of (NOS) and students' attitude towards science were high. Meanwhile, the results of analyzing the qualitative data from the focus group interviews of this study showed that there was a close convergence in the participants' understanding of (NOS). This result was supportive of the quantitative data from the (MONOS) scale. Accordingly, the researcher recommends adopting the use of (MS) in science curricula to encourage students to practice these strategies through standardized modules containing effective (MS) prompts to guide student's thinking processes during science lessons. She also recommends employing these strategies in training practicing teachers and preserve teachers to acquire understanding of (NOS). The researcher suggests that further research can extend the current study and address the impact of (MS) on different aspects of science teaching and learning processes