the study aims to examine the effect of Web Quests on improving academic achievement and critical thinking skills of 9th grade students in Science course at Al Batinah North Governance in Sultanate of Oman. The participants of this study using quasi-experimental method were composed of (60) ninth-grade students of Al Uhad School (5-9) at Al Batinah North Governance and divided into two groups; (30) students as experimental and (30) students as a control group. The study was applied over a six-week period during the second semester of the academic year 2016-2017. For this purpose, a study-based Web Quest website and an associated teacher guide were developed by the researcher and authentication of the content was verified by experts. An academic achievement test for 'space exploration'unit in science course was developed as a data collection tool. The test consisted of (20) items split into three different levels in which the reliability coefficient was found 0.70. In addition, Watson-Glaser critical thinking test consisting of (90) items which split into three different levels was applied in which the reliability coefficient was found 0.95 . Results showed that there was a statistically significant the mean difference between scores of both experimental and control groups in all levels of achievement test and in two of the three critical thinking skills (interpretation & Discussion evaluation) in favour of the experimental group (a=0.05). However, there was no statistically significant difference in (Deduction) skill between the experimental and control groups (a=0.05). It was seen that, in the light of the results achieved, Web Quest-based activities should be included in the curriculum for its importance in guiding students towards using Internet positively and effectively due to significant globalization and technological development. The study also proposes that different thinking skills of students should be improved and practised because thinking contributes to integrated individual personality so as to keep pace with the changing times