ABSTRACT Background: Testosterone (T) and estradiol (E2) play a critical role in male sexual function being essential for modulating libido and erectile function. We hypothesized that an imbalance of T/E2 ratio may be an important factor leading to the development of low sexual desire in ageing men. Objective: To evaluate the relationship between imbalance of T/E2 ratio and low sexual desire in ageing men. Patients and Methods: This study was conducted on 50 low sexual desire old men and 40 healthy control men (mean age 59.8 years & range 55-69 years). These men were subjected to history taking, clinical examination, sexual desire score of IIEF and SDI-2  as well as estimation of serum sex hormones (total T, free T, E2, prolactin, and SBHG) using ELISA method. Results: The sexual desire score of IIEF and SDI-2 were significantly lower in patients compared with the controls. The levels of   TT, E2, TT/E2, FT and FT/E2 were significantly lower among study group compared with the controls. On the other hand, there were significant positive correlations between FT and FT/E2 ratio and both sexual desire score of IIEF and SDI-2. SHBG, E2, TT/E2 showed poor AUCs (AUC = 0.651, 0.626, 0.685 respectively). FT/E2 showed fair AUC (AUC = 0.727). Serum FT showed good AUC (AUC = 0.882), TT, combined T/E2 and FT and combined TT and E2 showed excellent AUC (AUC = 0.900, 0.903, 0.958 respectively). Conclusion: Although older men with low sexual desire had significantly lower total and free T, our study failed to show significant correlations between total T, E2 or TT/E2 ratio and sexual desire score of IIEF and SDI-2. However, true androgen deficiency (FT) and true T/E2 imbalance (FT/E2 ratio) may have a role in discrimination between low and normal sexual desire in older men.