This research is that children's understanding of the concept of heavy and light is not optimal, it can be seen from the number of children 14 people 5 children can sort correctly, 9 other children have not been able to sort correctly at RA Hasanuddin Pontianak who has introduced the concept of heavy and light. The purpose of this study was to find out whether there is an understanding of the concept of heavy and light through weighing activities in children aged 5-6 years at RA Hasanuddin Pontianak Tenggara. This study uses a quantitative approach to the experimental method. Data collection techniques namely observation, documentation. The sample in this study was group B children, which consisted of 14 children. Testing the paired sample t test on the aspects assessed by the child between the pre-test and post-test, namely with an alpha significance level of 5% obtained a t-count value of -11,678 with a significance value of 0.01 which is less than an alpha of 0.05, so The decisions that can be made are rejecting Ho and accepting Ha, meaning that there is an influence on understanding the concept of heavy and light after the implementation of weighing activities in children aged 5-6 years.