Fennel (Foeniculum vulgare Mill.) is an economically important spice crop vulnerable to various insect pests, with aphids (Hyadaphis coriandari) being a major threat. This study aimed to assess the susceptibility of ten fennel genotypes/varieties to aphid infestation and identify those less susceptible to aphid populations. Results revealed significant variation in aphid populations among genotypes/ verities, with RF-290 exhibiting the least susceptibility and UF-219, UF-268, and UF-226 being highly susceptible. Morphological parameters like flowering time, umbel number, plant height, and maturity showed significant correlations with aphid populations. Total phenol content did not significantly affect aphid infestation, while soluble sugar content exhibited a positive correlation. These findings contribute to understanding fennel-aphid interactions and may aid in the development of pest management strategies for sustainable fennel production.