Reynoutria japonica is an invasive species, characterized by rapid growth and abundant biomass. It is undesirable in the environment due to its negative impact on other plant species and on the physicochemical properties of the soil in its surroundings. Current research concentrates mainly on the use of biomass of this species as a fertilizer or additive enriching the quality of compost. The aim of the study was to assess the chemical composition of R. japonica biomass from the suburban zone in terms of its use as an additive enriching the quality of compost. The results of the research indicate that both the leaves and stems of R. japonica were sufficiently rich in nutrients (N, P, K, Mg) and at the same time safe due to the small amounts of heavy metals contained in them (Zn, Cu, Fe, Mn). The values of the bioconcentration factor (BCF) for N, P, K and Mg in leaves and N, P and K in thin and thick stems were >1, which indicates that the above-ground biomass of R. japonica is a valuable source of macronutrients. At the same time, the BCF values for Zn were ~1.06, and for Fe, Mn, and Cu both in the leaves and in the stems were <1, which confirms that the above-ground biomass of R. japonica from the suburban zone is a safe and valuable component of compost, in which the analysed heavy metals will play the role of micronutrients. There were also highly statistically significant differences (p<0.001) in Zn and Mn content and (p<0.01) in the case of C, N, P, Mg, Fe and Cu between the leaves and stems of R. japonica.