The effects of topping method on the yield and major agronomic traits of two varieties, Sunwol and Youngjun of Alisma plantago, were investigated in the Southern region. Plant height, yield of fresh root, yield of dry root and weights of total roots were the highest in the variety of Sunwol, and at the plots with topping of four times cutting in flowering in main culm (Treatment No.1). Considering from our results, optimum topping method is most likly be topping of four times cutting in flowering in main culm in the Sunwol variety.