Experiments were conducted during potato winter seasons of 2007/08 and 2008/09 at Dakahlia, Egypt. Four potassium fertilization levels (0, 100, 150 and 200 kg/fed) were applied to clarify their effects on the population density of Myzus percicae (Sulzer), Aphis gossypii Glover, Aphis craccivora Koch, Bemisia tabaci (Gennadius) and Empoasca sp. in potato fields. The obtained results showed that the highest population densities of these pests occurred at no potassium fertilization (control) followed by 100 kg/fed and 150 kg/fed, respectively. The lowest population densities were recorded at 200 kg/fed treatment. A. gossypii and M. persicae were the most affected pests by potassium fertilization. A. craccivora and Empoasca sp. were affected in relatively moderate way. B. tabaci was the least affected one. On the other hand, epidermal thickness of potato leaves was significantly increased by fertilization level increase.