The results on the useful functional compounds of kenaf (Hibiscus cannabinus L.) leaves cultivated in reclaimed lands and the biological activity effects of extracts were as follows. On 98 days after sowing (DAS) Tainung-2 showed the highest total chlorophyll content (1.68 mg/g), and on 141 DAS Dowling showed higher chlorophyll content (1.50 mg/g) than the other two did. In all cultivars the total chlorophyll content was higher on 141 DAS than on 98 DAS. Total polyphenol and total flavonoid contents were the highest in Tainung-2 (30.50 mg/g and 57.03 mg/g, respectively), and total polyphenol and total flavonoid contents (30.50 mg/g and 57.03 mg/g, respectively) were the highest in 30% ethanol extraction. Ascorbic acid contents were higher on 141 DAS than on 98 DAS in three cultivars. SOD activities of kenaf leaf extract were generally over 90%. DPPH radical scavenging activity of Tainung-2 was higher than others.