Kudu (Pueraria lobata), a legume vine, has become a great concern in different parts of the world due to its invasive nature. It creates monospecific stand by outcompeting the existing flora. This species is very rich in secondary metabolites and adds substantial amount of litter into the soil due to its huge biomass turnover in every growing cycle. In recent studies, the allelopathic phenomenon of kudzu has been established. In the present study, we investigated the seasonal dynamics of phenolics in soil associated with the litter production and growth of kudzu plants in three spots along the banks of the Tama River, Japan. Seasonal variations of total phenolics in kudzu-infested soil were measured and checked whether the levels were allelopathically active. Kudzu litter was also allowed to be decomposed in laboratory for several weeks and at the end, the fate of soil phenolics was observed. Soil phenolic content under kudzu varied seasonally and the highest quantity was recorded in winter as an outcome of kudzu litter decomposition. On the basis of the field and laboratory investigation, it can be concluded that kudzu exert allelopathy through litter decomposition, and higher level of phenolics persist in soil for a considerable period of time.