As a neurosteroid hormone, vitamin D exerts multi-dimensional influence on the nervous system. It regulates synaptic transmission and synapse growth, as well as influences cognition and behaviors (Figure 2). Numerous epidemiological, molecular, and animal studies have revealed a link between vitamin D deficiency/insufficiency and an increased risk of ASD and ADHD. On the other hand, some studies demonstrated that vitamin D supplementation could reduce the symptoms in children with ASD and ADHD. Animal studies indicated that vitamin D might influence social process-related neural circuits like BLA-NAC and ACC-BLA pathways. Moreover, vitamin D might reduce the repetitive and aberrant social behaviors in ASD via regulating the mTOR pathway and oxytocin pathway. In addition, the prefrontal cortex circuits, as well as the dopaminergic and serotonergic pathways, which are frequently linked to the etiology of ADHD, may be impacted by inadequate vitamin D. More direct evidence on how vitamin D might affect the onset and progress of these disorders mechanistically is still missing. Nevertheless, vitamin D has the potential to be a treatment for neurodevelopmental disorders such as ASD and ADHD. It has the benefits including high safety, little side effects, and low cost. However, the precise therapeutic dose and effects, treatment duration and age of intervention for vitamin D remain to be determined. More clinical evidence is required before vitamin D can be extensively applied as a treatment strategy for ASD and ADHD. Most importantly, understanding how vitamin D contributes to the neurodevelopmental disorders will provide a solid foundation for the transition from the bench to the bedside.