T The study was conducted during two successive seasons 2019 and 2020 at Giza Governorate to evaluate the effect of some climatic factors (mean temperature and mean relative humidity) and phytochemical contents (nitrogen, phosphorus and potassium) on the population densities of principle pests, Bemisia tabaci (Genn.), Aphids (Aphis craccivora (Koch); A. gossypii (Glover) and Myzus persicae (Sulzer)) and Tetranychus urticae Koch. In festing common bean plants Phaseolus vulgaris L. in Egypt. Results showed that the activity of B. tabaci recorded two peaks in September and October in the first season, while it recorded only one peak in September in the second season. Aphids and T. urticae recorded only one peak during the first season on October and September, respectively, whereas it was recorded two peaks in the second season during September and October for the first pest and September for the second one. The population densities of B. tabaci and Aphids correlated negatively with mean Temperature in the two studied seasons, this relation was significantly negative in case of aphids. On the other extreme the population densities of T. urticae related significantly positive with mean temperature. The population densities of B. tabaci and aphids correlated positively with relative humidity in the two studied seasons, while the population density of T. urticae affected negatively with relative humidity in the two seasons. The population density of the three studied pests affected with the phytochemical component of common bean leaves. B. tabaci and aphids were correlated significantly negative with nitrogen, phosphorus and potassium in the two studied seasons, while the relationship between T. urticae population and the three tested phytochemical components was insignificantly positive with nitrogen and significantly positive of phosphorus and potassium in the two seasons. The combined effect (E.V. %) of climatic factors and phytochemical components on the population densities with the investigated pests was calculated separately and altogether using multiple regression analysis and showed that the combined effect of climatic factors on pest’s population densities were (46.00% and 48.70%), for both seasons respectively, while the combined effect of phytochemical components were (37.00% and 39.00%) respectively, in the two seasons. The combined effects of climatic factors and phytochemical components altogether were 39.50% and 45.40% respectively, for two studied seasons indicating that the mean temperature and mean relative humidity & phytochemical components of leaves may play a more important role in affecting on the population densities of the studied pests and this information’s can aid in the development of integrated pest management (IPM) of common bean plants.