The purpose of this study is to determine the effects of dynamic geometry software Geometer's Sketchpad (GSP) on students' achievement in symmetry of two dimensional shapes. A total of 36 mixed ability Year 3 pupils from a primary school in a rural area of Kedah participated in the study. They were divided into two groups: the experimental group was subjected to lessons shaped with Geometer's Sketchpad (GSP) while the control group was subjected to lessons using the traditional method. The difference between experimental and control groups' achievement was measured using post-test. Students' attitude toward learning of symmetry was measured using a questionnaire with a four-point Likert Scale. Results of the study showed that the experimental group performed better than the control group. These findings indicated that the use of Geometer's Sketchpad (GSP) improve the pupils' achievement and attitude towards learning symmetry of two dimensional shapes.