Host Plant's quality in the food chain of a herbivorous insect influences the insect's life performance, and thus abundance in its population. The effect of different ratios of N: K fertilization (40:60), (40:40), (40:0) kg/ha vs. control (0:0) were determined on chemical content parameters (N, K and C %) of the bean plant and as well on the performance of Aphis fabae Scop. Experiments were carried out in a greenhouse with 25±1?C, 75±5 RH and a photoperiodism cycle of 16 L: 8D hours. The highest percentages in plants tissue of N and K were found in plants fertilized with 40: 0 and 40: 60 (N: K) ratios respectively. Net reproductive rate (R0) of A. fabae fed on the mentioned treatments were determined as 14.75±2.4, 20.27±1.38, 22.07±2.2 and 17±3.1 female/female/generation, respectively. Intrinsic rate of increase (rm) of A. fabae on the four treatments were assessed as 0.215±0.017, 0.325±0.02, 0.295±0.014 and 0.258±0.017, respectively. Finite rates of increase (?) amounted to 1.32±0.001, 1.41±0.03, 1.38±0.01 and 1.32±0.001, respectively showing the daily rate of increase in aphid female population relative to that during the previous year. Mean generation times (T) in the four treats were 12.51±0.17, 9.32±0.17, 10.48±0.16 and 10.19±0.14 days. The results showed that there existed significant differences between R0, rm and ? of A. fabae different treatments (P<0.05). The highest rm and R0 were observed in treatments N: K with ratios of 40:40 and 40:0 showing that these treatments result in the most suitable best host plants for growth and development of A. fabae.