This study aims to analyse the Physical Activity (PA) levels of a group of children with ASD and explore certain socio-ecological variables that may be correlated with these levels. The participants of this cross-sectional study were 20 boys and 5 girls with ASD, aged between 4 and 14 years. A socio-demographic questionnaire was designed expressly to obtain socio-demographic data, and PA levels were measured with a triaxial accelerometer (ActiGraph, wGT3X-BT). After performing a descriptive analysis, we analysed the relationship between the variables through Spearman correlations and performed the Kruskal Wallis test to compare the results of moderate, vigorous and very vigorous PA according to the following factors: age, gender, PA of their parents or tutors, curricular adaptations, medication, number of siblings, attention deficit, impulsiveness hyperactivity, inattentive-ness, inability to achieve success, movement difficulties, learning difficulties and fearfulness. Finally, we performed logarithmic 4th-order regression analysis for the practice of moderate-intensity activity according to the participants' age. The findings show that variables in the individual domain (i.e. gender, age, co-morbidity/features of ASD and curricular adaptations) and family domain (i.e. presence of siblings and parents' PA) may be related to the PA levels of ASD children. This investigation shows the importance of considering socio-demographic aspects in children with ASD in order to promote healthy and active lifestyles.