Dogs are routinely exposed to events that may elicit stress and result in negative emotional states which can impact pet dog welfare. One event many dogs living with people are routinely exposed to is car travel, with many dogs displaying behaviors, along with corresponding physiological responses, that are indicative of stress and anxiety. There are a range of management and treatment options that exist from behavior modification, drug therapy and supplements, often with varying results. The aim of the present study was to evaluate whether multiple doses of a tetrahydrocannabinol (THC)-free cannabidiol (CBD) distillate over a period of six months could positively influence measures of stress in dogs. In a blinded, parallel design study, dogs (n=19) underwent a series of short car journeys (test) where a range of physiological and behavioral measures were collected pre, during and post-test. The car journeys elicited stress in this population of dogs, as indicated by significant changes (p<0.05) in several stress-related measures (serum cortisol, heart rate, heart rate variability, whining, lip licking, yawning and qualitative behavioral ratings) observed from baseline to test, which persisted over repeated car travel events. The mitigating effect of CBD treatment varied by measure, with cortisol, whining, lip licking and qualitative behavioral ratings indicating a significant (p<0.05) reduction in canine stress compared to the placebo group for at least one timepoint. Additional research investigating a range of dog populations and stressors, is required to fully understand the complex effect of CBD on canine emotional wellbeing.