Autism spectrum disorders (ASDs) include a variety of developmental brain disorders with clinical findings implicating the dysfunction of the left hemisphere. We generate mice lacking one copy of ASD-related genen Sh3rf2 and find that these mice recapture multiple ASD-like behavioral deficits. The Sh3rf2 haploinsufficiency resultes in abnormal excitatory synaptic transmission in the hippocampus, which is remarkably unilateral in the left hemisphere. Thus, our results support a notion that Sh3rf2 haploinsufficiency is a highly penetrant risk factor for ASD.