Abstract: To evaluate the allelopathy effects of benzoic acid and ρ-hydroxybenzoic acid on watermelon, this paper studied the effects of benzoic acid and ρ-hydroxybenzoic acid on watermelon seed germination and seedling growth by seed soaking, seed-bud soaking and seedling irrigation. The results showed that the seed germination percent decreased both in benzoic acid and ρ-hydroxybenzoic acid seed soaking treatments and the growth of hypocotyls and radicles in the seed-bud soaking treatments were inhibited significantly. The root vigor, height, diameter of stem, leaf area, shoot and root dry weight of the seedlings irrigated benzoic acid and ρ-hydroxybenzoic acid also decreaseded significantly. The inhibiting effects of benzoic acid and ρ-hydroxybenzoic acid increased with the concentrations. The results indicated that the benzoic acid and ρ-hydroxybenzoic acid had autotoxicity effects on watermelon seed germination and seedling growth.