The use of natural materials in the treatment is usually base empirical experiences from generation to generation based on information from an cestors. A study is necessary to find out and explain scientifically the activity of plant as an antimalaria drug. The purpose of this study was to determine the value of IC50 on the hem polymeritation inhibition activity assay of ethanol extract of C.tomentosa leaf. The inhibitory activity of heme polymerization in vitro did by Basillico modified method. The result of probit test of inhibition activity of hem polymerization of ethanol extract of C. tomentosa leaves has IC50 value of 1.179 ± 0.07 mg / mL and chloroquine diphosphate is 1.68 2 ± 0.03 mg / mL. T-test independent sample showed that there was no significant difference between IC50 extract value of ethanol leaf C. tomentosa with chloroquine diphosphate. Leaf ethanol extract C. tomentosa has inhibitory activity of hem polymerization. Key words: Heme Polymerization, Coptosapelta tomentosa Valeton ex K. Heyne, Manuran