Plant parasitic nematodes are among the most important limiting factors in crop production throughout the world. Root-knot nematodes (Meloidogyne spp.) are the most dangerous group of plant parasitic nematodes and more than 2000 plant species affected by these nematodes. Root-knot nematodes cause approximately 5% of global crop losses. The purpose of the present study was to determine the relationships between initial population (Pi) and final population (Pf) of M. javanica in three cucumber (Cucumis sativus L.) cultivars Super dominus, Bate-alpha and Sina roots and soil, as well as the effect of increasing Pi level of nematode on growth indices of cucumber cultivars under greenhouse conditions. The seeds of three cucumber (Cucumis sativus L.) cultivars were sown in plastic pots each containing 1000 g steam-sterilized sandy-loam soil. Four-leaf stage seedlings were inoculated with Pi densities of 0, 0.5, 1, 2, 3, 4 and 8 eggs and J2s of M. javanica per g of soil. The experimental design was completely randomized with four replicates under greenhouse conditions adjusted to 27 ± 4ºC under 16:8 h (light:dark) photoperiod. Plants were harvested 60 days after inoculation and plant growth parameters including shoot fresh and dry weight and shoot height were measured. Furthermore, number of eggs, galls and eggmasses per root system were counted. Finally, gall index (GI) and the reproductive factor (RF) of nematode were calculated. Results showed that in all cultivars, plant growth indices were reduced with increasing Pi of M. javanica so that shoot dry weight of Bate-alpha, Super dominus and Sina cultivars reduced 61, 73 and 89% at Pi of 8 nematode per gram of soil, respectively, as compared to control. The highest amount of RF was recorded at Pi=4 on Bate-alpha and Sina and Pi=2 on Super dominus cultivars. According to the Canto-Saenz’s scheme, Bate-alpha, Super-dominus and Sina cultivars at different Pi were classified as susceptible, showing GI > 2 and RF > 1.