It is argued that self-regulation skill is necessary both for displaying constructive behavior and for controlling negative social behavior, and self-regulation might affect social behaviors by increasing the ability to understand others' minds. In this research, in order to examine behavioral and cognitive aspects of self-regulation, we focused on both effortful control and executive function, and investigated their concurrent associations with socially competent and aggressive behaviors, and theory of mind (ToM). The participants were 212 preschool children in Turkey. We assessed executive functions with behavioral measures, and effortful control with mother reports. We used six tasks for comprehensive assessment of mental state understanding. Children's social competency and aggressive behavior were assessed with teacher reports. SEM results showed that when receptive language was controlled, ToM was significantly associated with social competence but not aggressive behavior. Both effortful control and executive functions were significantly related with social competency, aggressive behavior, and ToM; the pathways from each self-regulation skill were in similar strength. ToM was linked with social competence, but it did not have a mediating role in the relations of self-regulation with social competence. The findings highlighted the importance of self-regulation for socio-cognitive and social development in the preschool years.Keywords: Social competence, aggression, theory of mind, executive function, effortful control,preschool period.