Background: Although an inverse relationship between body mass index (BMI) and Parkinson disease (PD) has been repeatedly reported, to our knowledge, the relationship between BMI and antipsychotic-induced extrapyramidal symptoms (EPS) has rarely been studied in patients with schizophrenia. Our study aimed to evaluate the relationship between BMI and EPS in patients with schizophrenia. Subjects and methods: Using data from the Research on Asian Psychotropic Prescription Patterns for Antipsychotics (REAP-AP) study, we compared the prevalence of EPS in 1448 schizophrenia patients stratified as underweight, normal range, overweight preobese, overweight obese I, overweight obese II, and overweight obese III according to the World Health Organization (WHO) classification system for body weight status, and with underweight, normal range, overweight at risk, overweight obese I, and overweight obese II according to the Asia-Pacific obesity classification. Results: In the first step of the WHO classification system for body weight status, adjusting for the potential effects of confounding factors, the multinomial logistic regression model revealed that underweight was significantly associated with greater rates of bradykinesia and muscle rigidity, and a lower rate of gait disturbance. In the second step of the Asia-Pacific obesity classification, adjusting for the potential effects of confounding factors, the multinomial logistic regression model revealed that underweight was significantly associated with a higher rate of muscle rigidity. Conclusion: Findings of the present study consistently revealed that underweight was associated with a greater rate of muscle rigidity in a stepwise pattern among Asian patients with schizophrenia. Although the mechanism underlying the inverse relationship between BMI and muscle rigidity cannot be sufficiently explained, it is speculated that low BMI may contribute to the development of muscle rigidity regardless of antipsychotic "typicality" and dose in patients with schizophrenia.