Background: We aimed to investigate the relationship between maternal vitamin D and multivitamin supplementation during pregnancy and the risk of autism spectrum disorder (ASD) and symptoms in offspring with ASD. Methods: This study enrolled 1321 children with ASD and 1200 typically developing (TD) children under 7 years old in China. Maternal vitamin supplements were classified for vitamin D, multivitamin (with or without vitamin D), and none (no use of vitamin D or multivitamin). For children with ASD, symptoms were assessed with the Autism Behavior Checklist (ABC), Social Responsiveness Scale (SRS) and Childhood Autism Rating Scale (CARS), and neurodevelopmental levels were evaluated with the Children Neuropsychological and Behavior Scale-Revision 2016 (CNBSR2016). Results: Maternal vitamin D and multivitamin supplementation during pregnancy were both significantly associated with a decreased risk of ASD in offspring (P = 0.024 and P < 0.001). The ASD children born to mothers with gestational multivitamin supplementation had lower CARS [beta = -1.342 (-2.275, -0.409), P = 0.005] and communication warning behavior [beta = -6.631 (-9.899, -3.363), P < 0.001] scores and higher personal -social quotient [beta = 3.347 (0.190, 6.504), P = 0.038] than children born to mothers without supplementation. Maternal vitamin D supplementation was not associated with symptoms and development quotients in ASD children (P > 0.05). Conclusions: This study supports a protective association between maternal vitamin D and multivitamin supplementation during pregnancy and the risk of ASD in offspring. Maternal multivitamin supplementation may potentially moderate the symptoms and personal -social ability in ASD children. Further studies are needed on the role of maternal nutrition in the etiology and autistic symptoms and the underlying molecular mechanisms