This study was carried out to study effect of treated cucumber plants var. Cucumis sativus L.  by different concentrations of Triacontanol Hormone (TRIA) on the infestation by Aphis gossypii Glover at two locations (governorates), Giza overnorate and Qaluobiya Governorate during 2018 season under glasshouse conditions. Also, this study was carried out to study effect of treated cucumber plants by the same concentrations of (TRIA) hormone on the morphological characteristics and internal components of treated cucumber plants.  This study was carried out on three concentrations of Triacontanol Hormone, (25ppm), (35ppm) and (55ppm), beside fourth treatment which did not treat with any hormone (control). Results obtained showed that cucumber plants which treated with small concentration of (TRIA) (25ppm) were lower infestation by A. gossypii comparing to control. While cucumber plants which treated with medium concentration of (TRIA) (35ppm) were had no significant differences in the infestation by the same insect  compared to control, on the other hand cucumber plants which treated by high concentration of (TRIA) (55ppm) were higher infestation by the aphid compared to control.