This study was designed to evaluate the effects of Fasciolosis on serum testosterone profiles and semen characteristics of Yankasa rams. Twelve, apparently healthy, Yankasa rams aged 18-24 months were randomly divided into two groups (infected group A and control group B) with seven and five rams, respectively. The rams werekept under intensive management in different pens throughout the study period. Group A rams were inoculated with 800 metacecariae orally and monitored for 12 weeks Post Infection (PI). Clinical signs were manifested 2 weeks PI. Faecal examination revealed Fasciola eggs at week 7 PI in group A. Three mL of blood were collected aseptically via the jugular vein at 30 min interval, weekly between 08:00-9:00am for serum testosterone assay. Testosterone assay was done using ELISA technique. There was significant decrease in testosterone concentration in group A at different time intervals of the weeks of post-infection. The semen analysis showed the lowest mean (±SEM) of semen volume, semen motility, semen concentration, of group A, as (0.01±0.0 mL), (3.6±2.4%), (16.1±4.2%) compared to group B with mean (±SEM) (1.6±0.1 mL), (93.0±1.2%), (440.0±13.0%) at week 7 post- infection, respectively. This study revealed that Fasciolosis has a great impact on sheep mainly by diminishing their reproductive efficiency and rendering infected rams infertile. It is concluded that F. gigantica infectionhad advanced effects on testosterone production and semen quality of Yankasa rams.