This study compared the activity of the aerial part of P. japonicum with its root in order to examine the possibility of the medicinal use of the aerial part, which has not been used as medicine, in substitute for the root that has traditionally been used as medicine. For this purpose, the author measured the proliferation of Human $CD4^-$ T cells, which are related to immunity, the differentiation of HL-60 cells, and the contents of IL-6, IgE and $TNF-{alpha}$ and compared their anti-cancer effect on Hep3B and A549 cells. The results of this study are as follows: 1. As for Human $CD4^-$ T cells, $1.0;g/{ell}$ methanol extract from the aerial part promoted the proliferation of the cells 1.8 times higher while $1.0;g/{ell}$ methanol extract from the root did by 1.76 times higher compared to the control group. 2. As for HL-60 cells, methanol extract and water extract from the aerial part showed differentiation 1.14 times higher and 1.12 times higher respectively while methanol extract and water extract from the root did 1.14 times higher and 1.07 times higher compared to tile control group. 3. Cell density was highest on Day 4 of culture in all samples, Methanol extracts from the aerial part and the root showed activities of $7.9{ imes}10^3;cells/m{ell}$ and $7.5{ imes}10^3;cells/m{ell}$ respectively, and water extracts from the aerial part and the root did activities of $5.3{ imes}10^3;cells/m{ell}$ and $6.1{ imes}10^3;cells/m{ell}$. 4. The secretion of IL-6 was highest on Day 4 of culture. Methanol extracts from the aerial part and the root showed secretions of $6.7{ imes}10^{-3};pg/cells/m{ell}$ and $7.2{ imes}10^{-3};pg/cells/m{ell}$ respectively, and water extracts from the aerial part and the root did secretions of as high as $7.0{ imes}10^{-3};pg/cells/m{ell}$ and $6.0{ imes}10^{-3};pg/cells/m{ell}$. 5. As for the production of IgE, water extract from the root effectively inhibited the product at $1,000;{mu}g/m{ell}$, methanol extract from the root at $10;{mu}g/m{ell}$ and $100;{mu}g/m{ell}$, water extract from the aerial at $1,000;{mu}g/m{ell}$, and methanol extract from the aerial part at $1,000;{mu}g/m{ell}$. 6. According to the result of measuring the content of $TNF-{alpha}$, methanol extracts from the root and the aerial part showed inhibition effect at $10;{mu}g/m{ell}$, $100;{mu}g/m{ell}$ and $1,000;{mu}g/m{ell}$. 7. As for liver cancer cell Hep3B, $1.0;g/{ell}$ methanol extracts from the root and the aerial part showed inhibition effects of 78% and 70% respectively, and $1.0;g/{ell}$ water extracts from the root and the aerial part did inhibition effects of 56% and 59%. 8. As for lung cancer cell A549, $1.0;g/{ell}$ methanol extracts from the root and the aerial part showed inhibition effects of 75% and 70% respectively, and $1.0;g/{ell}$ water extracts from the root and the aerial part did inhibition effects of 48% and 45%. The results of this study presented above show that the aerial part of P. japonicum has immunizing and anti-cancer effects as high as its root, which has commonly been used as medicine. There should be more in-depth research on the aerial part of P. japonicum in the future.