Keratan sulfate (KS) is a glycosaminoglycan found mostly in hyaline cartilage, and it is a potential marker of hyaline cartilage catabolism. It has been recognized as a marker of early cartilage injury because of significant increases in concentration before macroscopic damage occurs. The objective of the current study was to assess the KS concentration in the serum of Arabian horses in the Equestrian Club, King Abdulaziz University, subjected to a training program, and correlate it to the resting baseline values. Serum Keratan Sulphate concentration was measured in twelve Arabian horses with a mean ± SD age of 36 ± 2 months subjected to a training program. The KS concentration was measured using an inhibition enzyme-linked immunosorbent assay (ELISA) using monoclonal antibody (mAb) 1/20/5-D-4. The results showed significantly higher values of keratan sulfate compared to the baseline values before training. Levels of serum KS showed a significant rise after 15 and 30 minutes of the training program. However, there was a notable reduction in the concentration of keratan sulphate discovered 60 minutes after exercise. This study showed transiently higher keratan sulphate levels in the serum of Arabian horses, which may be indicative of increased metabolic activities in joint cartilage due to joint overloading.