Serotonin (5-HT) plays a prominent role in a range of psychiatric disorders. Besides acting as a neurotransmitter, 5-HT is a neurotrophic factor during brain development, contributing to neurodevelopmental disorders (NDDs). Although neglected so far, the maternal 5-HTergic genotype may play a role in the offspring’s brain function and behavior, as both the placenta-derived 5-HT during pregnancy and the maternal care during early childhood. To initiate early intervention in NDDs, we aim to (1) understand the atypical development influenced by maternal 5-HTergic genotype, and (2) investigate if better maternal care induced by an enriched environment can be a non-pharmacological intervention. In our study, the well-established 5-HT transporter knockout (5-HTT-/-) rat is used to model 5-HTT gene variance in humans. Firstly, maternal behaviors in wild-type (5-HTT+/+) and 5-HTT-/- mothers were examined. Secondly, the neurodevelopmental trajectories of offspring with three 5-HTT genotypes (i.e., 5-HTT+/+, 5-HTT+/-, and 5-HTT -/-) were measured by tests assessing a series of social and emotional behaviors such as ultrasonic vocalizations from infancy to adulthood. Finally, the data was comprehensively analyzed to detect the correlations between maternal 5-HTT genotypes, maternal care, and the offspring’s behaviors across the genotypes and sexes. Our preliminary results show that the maternal 5-HTT genotype influences the offspring’s body weight and early behaviors in sex and genotype dependent manner during early postnatal days in a standard environment. The ongoing study is expected to uncover the differences in behavior features relevant to NDDs in the offspring with distinct genotypes under standard and enriched environments.