Background: Angelica gigas Nakai is a perennial herb belonging to the family Umbelliferae. Its roots are utilized in traditional medicine. The aim of this study was to increase the yield of and the content of two indicator components (decursin and decursinol angelate) in A. gigas Nakai. Methods and Results: The roots of A. gigas Nakai were harvested 4-times from late August to late October in 2017. Two agents (trace element-TE, and plant hormone-HM) were applied 4 times at intervals of 2 weeks. The content of the two indicator components were analyzed by high performance liquid chromatography. The HM treatment showed the greatest increase in underground part yield and root diameter. The content of the two indicator components in the control (non-treatment) group was the highest in the underground part, but was higher in the aerial parts in the agent treatment group. After treatment with the agents, the content of the indicator components tended to decrease in the underground part. However, the total content of the indicator components in the two agent treatment groups exceeded the level of 6% set by the Korean Pharmacopoeia. Conclusions: The highest underground part yield was found in the HM treatment group, while the highest content of decursin and decursinol angelate were found in the control group. This study provides basic information for yield improvement in A. gigas.