Competition horses are susceptible to high stress levels. Lavender aromatherapy (LA) is legal, has the potential to reduce stress, and is a relatively unexplored area of equine physiology. We hypothesis that LA has positive effects on helping horses cope with stress. We predict that these effects can be measured in lowered cortisol, norepinephrine, and heart rate levels in horses that have been subjected to lavender aromatherapy during a stressor. Eight horses were used in a crossover study and were transported for 15 minutes in a horse trailer. During the trailer ride (stressor), the horses received water aromatherapy as the control, and LA as the treatment. Three measurements of heart rates and blood draws were taken on each horse: (1) baseline—before loading into the trailer, (2) stressed—immediately after the trailer ride, and (3) recovery—50 minutes after the trailer ride. The blood samples were used to quantify serum cortisol levels. In both the control and treatment horses, the average difference between the baseline and stressed measurements of heart rate (HR) and cortisol increased when the horses were transported (control HR = 10.6 b/m ± 2.6 standard error [SE]; treatment HR = 9.3 b/m ± 2.6 SE; control cortisol = 3,747.2 pg/uL ± 864.2 SE; treatment cortisol = 2,511.8 pg/uL ± 1009.9 SE). In the control and treatment horses, there was no difference in the HRs of the control and treatment horses (P-value = .37); there was a difference in cortisol levels (P = .038), which provides evidence to conclude that cortisol levels were lower in horses that were subjected to LA during a stressor.