To study the best harvesting time of summer-planted Isatis indigotica Fort.,we planted different cultivated populations,which were from Shanxi,Anhui,Gansu,Jiangsu and Henan Province,by pot culture experiment.Test samples,which were sampling interval 10 days since growing 60 days,were harvested for 6 times.The contents of indigo and indirubin in their leaves,petioles,rhizomes and roots were determined by HPLC.The results showed that:(1)The biomass of leaves,petioles,rhizomes and roots increased with the growth time,in which the growth was the best,and dry matter accumulation was the maximum is the population from Shanxi.(2)The highest contents of indigo and indirubin in leaves and petioles of different populations occurred 90~100 days,namely a peak period of active components in leaves.(3)The highest of indigo accumulating amount (dry weight multiplying indigo content) in leaves of every population of I.indigotica appeared at 90~100 d,and the highest of indirubin accumulating amount in leaves,petiole and rhizome appeared at 90~100 d too.The most appropriate sampling time of I.indigotica from Shanxi,Anhui and Henan was 100 days,while the Gansu and Jiangsu populations were sampling at 90 days,taking indirubin as the quality control indicator in China Pharmacopoeia,meanwhile taking comprehensively the biomass and accumulating amount of active component as comprehensive indicators.