AIM: The purpose of this study is to determine the effects of calcium supplementation to decrease blood lead levels (BLLs) of children at high risk for chronic lead poisoning and to determine its effects on short-term memory. MATERIALS AND METHODS: Children aged 8–12 years lived in the highest traffic density in Medan randomly included in this quasi-experimental study, divided into two groups (control and supplementation group received tablet contain four hundred milligrams oral calcium twice daily for 3 months). Samples for BLLs were collected before and after 3 months of supplementation, and short-term memory measurements are carried out by picture and forward digital span test. Descriptive statistics were calculated at baseline and 3 months; comparison between before and after treatment was assessed with t-tests, p < 0.05 considered statistically significant. RESULTS: BLLs samples, who are exposed to lead for >6 months were ranging between 0.4–12 μg/dL. Median BLLs in supplementation group before treatment was 2.1 μg/dL and after treatment was 0.01 μg/dL (p < 0.01); difference between median in BLLs after treatment in supplementation group was 2.090 μg/dL (p = 0.004). Score memory picture in the supplementation group before treatment was 61.4 ± 24.83 and after treatment was 76.21 ± 15.97 (p<0.01). Score memory digital span in the supplementation group before treatment was 5 (3–7) and after treatment was 7 (5–7) (p < 0.01). CONCLUSION: Three months of oral calcium supplementation 400 mg twice daily for high-risk chronic lead poisoning children reduced BLLs significantly and improved their short-term memory.