Maternal diet is a key determinant of later child’s metabolic and mental health outcomes. Human and/or animals consuming a western diet (WD), as compared to a healthy diet (HD), exhibit microbiota dysbiosis, low-grade inflammation, behavioral alterations and defects in the central reward circuit. Accordingly, epidemiological studies show that WD consumption during pregnancy is associated with adverse metabolic and mental health outcomes in offspring. We have developed a mouse model to study the impact of maternal WD on the offspring and challenged hypotheses related to dysbiosis, inflammation and reward circuit alteration hypotheses in this model.While control mice were fed with standard chow (HD), WD-fed female mice received in addition at least two different sugar- and fat-rich food elements, starting one week before mating and continuing until weaning. Compared to pups born from HD-fed mothers, pups born from WD-fed dams exhibited increased weight gain, accelerated development, hyperactivity, and social interaction deficits in the early postnatal period. Behavioral impairments persisted in adulthood. Additionally, we found microbiota composition alterations, increased brain proinflammatory cytokines, and deregulated expression of reward-related genes in the nucleus accumbens in WD offspring. To test the contribution of these different processes to the phenotype of WD-fed mice, we assessed the effects of anti-inflammatory treatment, fecal microbiota transfer and probed the cellular transcriptional phenotype of the nucleus accumbens using single cell RNA sequencing. Our results provide evidence of a tight intertwining of different physiopathological processes underpinning the deleterious influence of WD on neurodevelopment.