The purpose of this study is to evaluate the performance of student achievement during comprehension lesson using metacognitive strategy and examine the effects of the strategy used in reading and understanding expository text lessons. Besides, this study also identified metacognitive strategy used by students in all three reading processes (before reading, during reading and after reading). The research applied a quasi-experimental design. Research sample involved Standard 4 students from a government primary school in Muara Brunei District. Samples were divided into two groups, namely the experimental group and the control group. Each group involved 30 average-ranking students. Research results were analysed using independent t-test samples to assess the significant differences for mean of reading comprehension performance between control group and experimental group during pre and post-tests. Meanwhile One Way Ancova analysis was used to determine the effects of using metacognitive strategy during reading comprehension lessons. Based on the t-test analysis, there was a significant difference of reading comprehension performance between the score of experimental group and control group, t = 12.96, p < 0.0. The analysis of One Way Ancova data, p= 0.00 < 0.05 (F " ratio = 493.22/2.25 = 219.41 p < 0.05) also proved that the significant effects of metacognitive strategy usage on comprehension lesson. Overall, the metacognitive strategy used by the students in this study has proven to enhance students' understanding on the texts that they have read.