Urinary Na+/K+ ratio has been shown to be a very useful tool in assessing the daily intake of sodium and potassium. Reports have also shown an association between blood pressure and urinary Na+/K+ ratio (Hedayati et al., 2012). Aldosterone regulates the renal reabsorption of Na+ and the secretion of K+ (Wiederholt et al., 1972) thus a major determinant of urinary Na+/K+ ratio. This study aims to assess gender difference in urinary Na+/K+ ratio and aldosterone excretion in urine before and after furosemide administration. We investigated Na+/K+ ratio and aldosterone excretion in 24hour (24h) urine and 12h (7am-7pm, D; and 7pm-7am, N) urine samples with and without furosemide administered. Ethical approval was obtained for 20 healthy subjects (10 males and 10 females) aged 20-30 years for this study. On the first day, 12h (D), 12h (N) urine were collected. Thereafter, 20mg oral dose of furosemide () was given to subjects twice at 7am & 7pm on the second day. 12h (D and N) urine samples were collected. 24h urine samples were obtained from both 12h samples. Na+ and K+ were analyzed using flame photometry; while urine aldosterone concentration was analysed using the enzyme immunoassay method (DRG International, Inc, USA). Values are expressed as Means ± S.E.M and analyzed using unpaired Student’s t-test. Females had higher baseline Na+/K+ ratio than males in 12h-D (6.09±1.03 vs. 2.9±0.28; P<0.001) 12h-N (7.78±0.49 vs. 4.28±0.3; P<0.001) and 24h (6.6±0.65 vs. 3.63±0.24; P<0.001) samples. Administration of furosemide caused dieresis and significant increase (P<0.001) in the urinary Na+/K+ ratio in the timed urine samples (12h-D, 12h-N and 24h) in the male subjects. Although the baseline urinary aldosterone excretion in all timed urine samples were similar in both males and females, the 24h urinary aldosterone excretion after furosemide administration increased only in males (P<0.05). We conclude that there is a gender related difference in the urinary Na+/K+ ratio and that this difference was abolished by furosemide administration.