Background: According to WHO research, there are approximately 24 million people living with schizophrenia worldwide and schizophrenia is characterized by a combination of psychotic and non-psychotic symptoms. Since the cause of the disease is not fully understood, antipsychotic medications are used as symptomatic treatment. According to the 2022 statistics of the NCMH, 718 people with schizophrenia are being treated under active surveillance in Mongolia. The reason for conducting this study is that the manifestation of drug side effects resulting movement disorders in patients with schizophrenia, which has not been studied in Mongolia. Aim: To investigate the relationship between adherence of medication regimen and abnormal involuntary movements in patients with schizophrenia. Materials and Method: The study was conducted using a descriptive method, cross-sectional design, purposive sampling with the questionnaire and standardized tests. Ethical approval for this study was approved by the NCMH (№3/77 30th of January, 2023) and Research Ethics Review Committee of MNUMS (№2023/3-02). Each participant was asked to complete 5 groups of 36 questionnaires, and standard tests were used to assess patients’ adherence to medication regimens (Morisky scale) and abnormal involuntary movement scale (AIMS). The study was conducted between March and August 2023, and the results were summarized and analyzed using STATA 14 software. Results: The study included 209 patients with schizophrenia, aged 18-79 years, of whom 47.4% (n=99) were male and 52.6% (n=110) were female (p=0.21). Of the participants, 28.2% (n=59) had less than secondary education, 76.5% (n=160) were unmarried, and 85.2% (n=178) had a disability due to mental health. 32.5% (n=68) of the patients with schizophrenia in the study used a combination of typical and atypical medications, and the most commonly used antipsychotic drugs were haloperidol (30.6%), chlorpromazine (26.8%), levomepromazine (25.8%), risperidone (24.4%), and quetiapine (21.1%). 1.4% (n=3) of the patients had good, 52.6% (n=110) had moderate, and 45.9% (n=96) had poor adherence to the medication regimen (Cronbach’s α=0.781). However, according to the results of the test for assessing abnormal involuntary that are performed without self-control, 49.76% (n=104) responded that they felt more sensitive to facial and oral movements, and 44.5% (n=93) to limb movements. The patients’ adherence to the medication regimen was statistically significant with facial and oral movements (n=104; p=0.036) and general body movement disorders (n=94; p=0.05). Conclusion 32.5% of patients with schizophrenia were taking typical and atypical antipsychotics, and 45.9% had poor adherence to medication regimens and were more likely to exhibit clinical forms of abnormal involuntary movements, including facial (p=0.036) and general movement disorders (p=0.05).