Abstract: Ratings on 36 personality descriptive adjectives were made on 100 companion horses by owners, trainers, and stable managers. The descriptors had been previously provided by a subset of 30 raters based on their own experience with horses. Principal components analysis revealed three statistically significant factors accounting for 59% of the variance. The first was a large, complex factor resembling the human Agreeableness factor. This factor contained four clusters of items reflecting obedience, kindness, sociality, and non-aggressiveness. The second factor resembled human Extraversion, although it also contained items reflecting intellect and curiosity. The third factor reflected Neuroticism or Emotionality. Factors similar to Agreeableness, Extraversion, and Emotionality are frequently observed in other taxa. The diverse composition of the Agreeableness factor indicating covariation among obedience, kindness, sociality, and non-aggressiveness may be a result of the intense artificial selection for all four components during the 6000 years of horse domestication.