Nowadays, plastics overflows everywhere such as in tropical rain forest far from our residential area, or the river in our living areas. Plastics reduce the biomass of plant when it is contained in the soil, but the previous research never show the actual concentration happening the reduction of biomass. Now, Ministry of Agriculture, Forestry, and Fisheries in Japan promotes farmers to use biodegradable plastic mulches and mix with soil after using up, so the risk happening soil plastic pollution increases. Thus, we set the growth experiment of Japanese Mustard Spinach (Brassica rapa L. var. perviridis) in the hydroponic environment polluted by plastic bags. We used two types of seeds from Sakata Seeds and Takii Seeds companies, and two types of plastic bags which are non-biodegradable and 30% biodegradable shopping bags. The concentration of plastics is 0%, 1.5% and 3.3%, then the growth of Japanese Mustard Spinach is compared. The result shows there is no significant difference of growth in each environment. Then, the growth is reduced when plastic touches with the plants’ roots. In this way, in the less contaminated areas, the physical effects by plastics is more likely to happen negative effects on the plants’ growth.