Abstract: Root knot nematode (RKN, Meloidogyne incognita) is a serious disease in tomato production. The effect of RKN initial population densities on the tomato height, the number of leaves, the number of flower spikes, the fresh and the dry weight of plant were evaluated in pot experiments under the greenhouse condition to understand the effect of population density on the pathogenic potential of M. incognita in tomato. The results showed that the plant height, the number of leaves, the number of flower spikes, and the fresh and the dry weight of plant were decreased with increasing densities of M. incognita, but the disease index was increased. The T value (tolerance limit) was calculated based on the plant height, fresh weight, dry weight with the Seinhorst model. The final tolerance limit of tomato to RKN was determined as 4.4 nematodes per milliliter soil. There was some damage to the root, but no obvious influence on the growth of tomato was observed when the nematode densities were lower than tolerance limit.