Background: Familial psycho-education is a training model dedicated to providing essential information and educating families with a psychiatric patient to work with mental health professionals as part of a treatment plan for their ill family members. Objectives: Our aim of this study was to investigate the effectiveness of the family psychological didactic program as an adjunctive treatment to medication in hospitalized patients with schizophrenia to reduce negative and positive symptoms. Methods: In this clinical trial, we included 49 Iranian inpatients with a diagnosis of schizophrenia hospitalized at Shiraz Psychiatric Hospital from September 2016 to May 2017. They were randomly assigned to experimental (n = 24) and control (n = 25) groups. All groups were prescribed their usual pharmacological treatments. Additionally, in the experimental group, a psychological education intervention was planned for their families. This intervention consisted of six 90-minute sessions that lasted for three weeks. Before the intervention, after the intervention, and two months after the intervention, all subjects completed the Positive and Negative Syndrome Scale (PANSS). Results: This study was undertaken on 50 hospitalized schizophrenic patients. Most were male (72%). The mean PANSS scores at the pretest and posttest were 82.5 ± 12.594 and 84.72 ± 9.629 for the intervention group and 50.08 ± 11.477 and 51.92 ± 9.823 for the control group, respectively. Based on the ANCOVA, all groups showed the same decrease in the posttest PANSS score, although there was no considerable difference among the groups (F = 0.049; P = 0.825) in the posttest. Nevertheless, eight weeks after the completion of the intervention program, the severity of symptoms was significantly reduced in the intervention group compared to the control group. (F = 165.931; P = 0.001). Conclusions: The family psychological training intervention as an additional treatment for hospitalized patients with schizophrenia can increase the effectiveness of drug treatment. Of course, we must consider the small research sample when generalizing the results.