The history of Yabusame (traditional Japanese mounted archery) as a modern sport is short, and only a few physiological studies have been conducted on the horses used. Therefore, this study investigates changes in blood cell composition and lactate levels of Hokkaido native horses used for Yabusame to determine whether the current exercise regimens are appropriate. We conducted the same experiment at two Yabusame horseback riding facilities, each using four horses of the Hokkaido native breed. In Experiment 1, blood samples were taken at three time points (while stationary, after preparatory exercise, and after horses had cantered five times on a 170 m track to simulate the Yabusame competition). In Experiment 2, blood samples were taken at four time points (while stationary, after walking for ~10 min to the racetrack, after preparatory exercise, and after cantering five times on a 150 m track to simulate competition). Lactate Pro and a blood cell counter were used to measure lactate levels and blood cell components, respectively. In Experiment 1, lactate concentration, red blood cell count, and hemoglobin were significantly (p<0.05) higher after exercise than the baseline. In Experiment 2, both lactate concentration and hemoglobin levels rose significantly (p <0.05) from stationary levels after walking to the track and performing the preparatory exercise. However, lactate concentration remained within the physiological range (<4 mmol/L, a threshold that indicates fatigue in horses) even after the elevated physical activity. Therefore, the exercise tested in this study did not impose an excessive physiological burden on the horses.