The aim of this study was to investigate the effect of plant growth at several different growing periods on antioxidant activities and zeatin and ABA contents of Artemisia iwayomogi. Measurements of antioxidant activities, lipid peroxidation inhibition, and superoxide radical scavenging activity were done using PMS, NBT and lipid auto-oxidation analysis, respectively. The results show that activities of antioxidants from Artemisia iwayomogi had much higher than BHT. DPPH free radical scavenging effect of Artemisia leaf extract was increased from $71.06{pm}4.36%$ in April to $90.06{pm}4.41%$ in October. Activities of superoxide radical scavenging and lipid peroxidation inhibition were $33.83{pm}3.45%$ and $45.60{pm}3.10$ in April and then increased to $84.40{pm}4.00%$ and $75.86{pm}3.50%$ in October, respectively. An ELISA technique has been developed for the determination of zeatin and ABA in Artemisia leaves. By this method, the content changes of zeatin and ABA from Artemisia during the growth were investigated. The zeatin content in leaf was measured to be $186.86{pm}1.40$ pmol/g dry weight in April, however, decreased to $117.93{pm}5.83$ pmol in October. The ABA content in leaf increased from $19.00{pm}1.26$ nmol in April to $68.20{pm}2.52$ nmol in October. Relationship between antioxidant activities and plant hormone contents was indicated that antioxidant activity may depend on decreasing zeatin content or increasing ABA content.