Sensory processing abnormalities, anxiety and restricted and repetitive behaviours (RRBs) frequently co-occur in Autism Spectrum Disorders (ASD). Though the relationship between these phenomena is not well understood, emerging evidence indicates intolerance of uncertainty (IU) may play an important role. This study aimed to determine pathways between sensory abnormalities and RRBs, and the role anxiety and IU may have. We gathered caregiver report data for 53 children with ASD aged 8-16 years. We found sensory "under" responsiveness and sensory "over" responsiveness were significantly associated with repetitive motor and insistence on sameness behaviours, and the relationships significantly mediated by IU and anxiety. Our findings indicate different mechanisms may underpin repetitive motor and insistence on sameness RRBs, which can inform treatment interventions.