Aqueous and methanol extracts of different kudzu organs (leaf, stem, root and seed) were assayed by using lettuce, radish and perennial ryegrass seeds for allelopathy. Both leaf and root extracts inhibited all germination indices studied (total germination, speed and accumulated speed of germination, and coefficient of the rate of germination). The results suggest that reduction of water imbibition is the primary mechanism of germination retardation. Seedling growths of the test species were also reduced by leaf and root extracts. However, radicle growth was more sensitive than hypocotyl to toxicity. Root respiration and chlorophyll synthesis in lettuce, radish and perennial ryegrass seedlings were also hindered by leaf and root extracts. Although the sensitivity of the species varied due to the extractants, leaf posed the highest degree of inhibition in all cases. Phytotoxic effects of kudzu litter and rhizosphere soil were tested by modified sandwich and rhizosphere soil method, respectively with the above mentioned test species. Both litter and rhizosphere soil of kudzu significantly inhibited the growth of root and shoot of all test species studied. The result from this study suggests that allelopathy of kudzu may be one of the possible mechanisms of invasion which is primarily accomplished by retarding neighboring species seed germination and seedling growth.