In this study the antioxidant activity of C. iners leaves standardized extract was evaluated. Cinnamomum iners leaves (methanol extract, chloroform fraction and subfraction 1) was standardized using cinnamic aldehyde. The phenolic and flavonoid content of C. iners leaves and cinnamic aldehyde were determined in this study. In addition, the antioxidant potential of C. iners leaves was evaluated using DPPH (2,2-Diphenyl-2-picryl-hydrazyl) free radical scavenging method, hydrogen peroxide decomposition study and reducing power assay. This study showed that C. iners leaves standardized extract showed promising antioxidant property.