Children with autism spectrum disorder (ASD) experience moderate to profound challenges in relation to the skills required for social participation. Animal-assisted intervention (AAI) is increasingly used within early community care. However, the results of its early application in this population group are not known. This pilot study aimed to explore the feasibility of an early intervention based on the use of therapy dogs and to examine their impact on communication and social interaction skills. A within-subject quasi-experimental longitudinal design was used. The instruments for measuring results were the Assessment of Communication and Interaction Skills (ACIS)and Animal-assisted Therapy Flow Sheet, both based on observation. A total of 19 children with confirmed or probable ASD (with mean age of 46.2 months), cared for in a Spanish therapeutic unit, participated in a median of nine AAI sessions, with a mean duration of 19.9 min per session. The total ACIS score increased significantly between the initial and final assessments of the study, with communication and social interaction skills improving with a large effect size. In the Animal-assisted Therapy Flow Sheet instrument, statistically significant improvements were found in most of the items that evaluate the frequency of child-dog social relationships (look at the dog, touch it, talk to it and get involved in an activity with the animal) and child-therapist relationships (look at the therapist and talk to him/her); the effect sizes ranged from medium to large. In conclusion, the early application of an AAI is feasible and seems to improve communication and social interaction skills, both essential elements for social participation. The results suggest that this intervention may be a beneficial non-pharmacological therapy as a complementary approach within community care for children with ASD in the early years of their life. K E Y W O R D S Animal assisted Therapy, autism spectrum disorder, communication, early intervention, interpersonal relations | 1221 ÁVILA-ÁLVAREZ Et AL. S U PP O RTI N G I N FO R M ATI O N Additional supporting information may be found online in the Supporting Information section. How to cite this article: Ávila-Álvarez A, Alonso-Bidegain M, De-Rosende-Celeiro I, Vizcaíno-Cela M, Larrañeta-Alcalde L, Torres-Tobío G. Improving social participation of children with autism spectrum disorder: Pilot testing of an early animalassisted intervention in Spain. Health Soc Care Community.