Experiments were conducted to estimate the susceptibility of two apple cultivars (Anna and Golden dorset) to infestation with Panonychus ulmi Koch (Acari: Tetranychidae) and its population fluctuation during the two successive seasons, 2012 and 2013 at Menoufia governorate. The results showed that, Anna cultivar was the most highly susceptible recording average of 7.34 and 10.5 mite moving stages/leaf during the two successive seasons, respectively. The lower infestation was recorded with Golden dorset cultivar, being 1.6 & 7.49 mite moving stages/leaf during the two successive seasons, respectively. Susceptibility of apple cultivars to infestation with P. ulmi may be affected by plant leaf morphological structure and its chemical contents. The density of trichomes of Golden dorset cultivar was higher than that of Anna cultivar, the less density of trichomes the more mite infestation. Also, when the level of total phenolic compounds increased the infestation percentage decreased, while no effect of Tannins occurred. Mite populations reached its peak during May and April in the first and second seasons, respectively, and infestation was lower in the first season.