Small hippocampal size may be implicated in the pathogenesis and psychopathology of schizophrenia (SCZ). However, does the volume of hippocampal subfields in SCZ patients affect response to antipsychotic treatment? In this study, we used risperidone to treat first-episode drug naive (FEDN) SCZ patients for 12 weeks, and then explored the relationship between baseline hippocampal subfield volumes, as well as any changes in these hippocampal subfield volumes during treatment, and improvement in their psychopathological symptoms. By adopting a state-of the-art automated algorithm, the hippocampal subfields were segmented in 43 FEDN SCZ inpatients at baseline and after 12 weeks of risperidone monotherapy, as well as in 30 matched healthy controls. We adopted the Positive and Negative Syndrome Scale (PANSS) to assess psychopathological symptoms in patients at baseline and at post-treatment. Before treatment, SCZ patients had no significant differences in total or subfield hippocampal volumes compared with healthy volunteers. However, we found a significant correlation between a smaller left CA1 at baseline and a lower PANSS total score and general psychopathology sub-score at post-treatment (both p < 0.05). Furthermore, the left CA1 at baseline was significantly smaller in responders, who had >50% improvement in PANSS total score, than in non-responders (p < 0.05). Our results suggest that smaller left CA1 volume may be a predicator for improvement in psychotic symptoms of FEDN SCZ patients.