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In Korea, root-knot nematodes, Meloidogyne incognita, have caused serious damage to oriental melon production, especially in Gyeongsang province, Korea where oriental melon has been cultivated without fallowness. In this paper, its economic importance has been studied. The effect of pre-plant population levels (Pl) of M. incognita at second stage juvenile (J2) on oriental melon was investigated. Thirty days after planting, the length of secondary vines and number of leaves tended to decrease with increase of population density of M. incognita. This indicates the lower Pl of M. incognita, the better growth of oriental melon acquired. The mean number of leaves was 14.6 at the low Pl whereas 12 at high Pl, indicating that the growth of oriental melon was negatively affected by high Pl. The Pl of M. incognita was negatively correlated with stem diameter, leaf area, and ovary length, while positively correlated with the day required for fruit set. The mean number of fruits per plant was 5.8 at low Pl, 5.4 at medium Pl, and 5.0 at high Pl. The mean number of marketable fruits decreased as Pl of M. incognita increased (5.1 at low Pl, 4.7 at medium Pl, and 3.0 at high Pl). The weight and width of fruits were negatively influenced by the increase of Pl levels. An appearance index, a major standard of evaluating fruit quality, decreased when the Pl levels increased but soluble solid contents were not affected by Pl levels.