Experiments were conducted to evaluate the susceptibility of three muskmelon cultivars (Ananas France, Galia2 and Shahd2) to infestation with Tetranychus urticae Koch and its population fluctuation during two successive seasons (2012 and 2013) at Behira governorate. Galia2 cultivar was the most highly susceptible recording average of 97.16 and 100.3 mite moving stages and 86.38 and 74.20 eggs/leaf during the two successive seasons, respectively followed by Shahd2 cultivar recording 86.16 and 86.43 mite individuals during the two seasons, respectively. The lowest infestation was recorded on ananas france registering 41 and 39.40' during the two successive seasons respectively. Susceptibility of muskmelon cultivars to infestation with T. urticae may be affected by its chemical contents. Negative relationship occurring between motile mite infestation levels and total Alkloids; while no correlation for eggs with all components. Mite population reached its peak during April in the two successive seasons.