The effects of postweaning social isolation (pwSI) on the morphology of the pyramidal neurons from the medial part of the prefrontal cortex (mPFC) and hippocampus were investigated in rats. The animals were weaned on day 21 postnatal (P21) and isolated 8 weeks. After the isolation period, locomotor activity was evaluated through 60 min in the locomotor activity chambers and the animals were sacrificed by overdoses of sodium pentobarbital and perfused intracardially with 0.9% saline solution. The brains were removed, processed by the Golgi-Cox stain and analyzed by the Sholl method. The locomotor activity in the novel environment from the isolated rats was increased with respect to the controls. The dendritic morphology clearly showed that the pwSI animals presented a decrease in dendritic length of pyramidal cells from the CA1 of the hippocampus without changes in the pyramidal neurons of the mPFC. However, the density of dendritic spines was decreased in the pyramidal cells from mPFC and Hippocampus. In addition, the Sholl analyses showed that pwSI produced a decrease in the number of sholl intersections compared with the control group only in the hippocampus region. The present results suggest that pwSI may in part affect the dendritic morphology in the limbic structures such as mPFC and hippocampus that are implicated in schizophrenia.