Abstract The purpose of this study was to improve students’ conceptual understanding of division through chunking strategy. Quasi- experimental, especially single groupdesign with both quantitative and qualitative approach was employed in this study. The design is an appropriate way to answer the research questions and achieve the research objectives.The participants of this study were 52 third grade students(one section (A) out of four grade three sections). The quantitative data were obtained through conceptual understanding test and the qualitative instrument constituted of observation and interview. The obtained quantitative data were analyzed using Paired Sample t-test. The qualitative data were analyzed based on narration. Significant mean differences were observed on the pre and post-test results of students in favor of the post test.It revealed that students’ conceptual understanding of division of whole numbers improved. Similarly, the observation and interview results compared between after intervention and before intervention in students conceptual understanding of division of whole numbers exhibited substantial changes in using chunking strategy. From the results of this study, it is possible to conclude that chunking teaching strategy is supportive for improving students’ conceptual understanding of division of whole numbers. But the researcher faced some major challenges when she hastaught division by using chunking strategy. For example; students’ had prior knowledge gap about addition, subtraction, and multiplication.Then when they applied the new strategy to solve a large numbers they sometimes took list number among the multiples of the divisor and when they manipulated the repeated subtraction they went long steps.From the result of this study, it is possible to conclude that chunking teaching strategy improves students’ conceptual understanding of division of whole numbers.In light of finding address by the researcher the recommendations forwarded so as to apply chunking strategy in the teaching learningprocessand to minimize the problem that difficult to the students’ conceptual understanding. KEY WORDS: chunking strategy, conceptual understanding, division, and design based research,