Background: Even though United Nation announced that all persons with a mental illness shall be treated with humanity and respect for the inherent dignity of the human being, up to now, the use of coercion (physical restrain) is still considered as unavoidable in managing abnormal behavior of psychiatric patients. But, there is no information regarding the magnitude and contributing factors of physical restrain among bipolar patients in low-income countries like Ethiopia. Methods: A cross-sectional study was conducted at Amanuel Mental Specialized Hospital from May 1 to June 1, 2015 among 400 participants who were selected by systematic random sampling technique. Data were collected by interviewing; adjusted odd ratios (AOR) with 95% confidence intervals (CI) were used and p value <0.05 was considered as statistically significant. Results: The prevalence of physical restrain was 65%. Factors like, having two or more episodes [AOR = 1.84 95% CI (1.16, 2.93)], history of aggression [AOR = 2.14, 95% CI (1.26, 3.63)], comorbid illness [AOR = 1.76, 95% CI (1.26, 3.63)], use of antipsychotic [AOR = 1.79, 95% CI (1.08, 2.95)] and current use of Khat [AOR = 1.83, 95% CI (1.10, 3.04)] were associated significantly. Conclusions: The prevalence of physical restraint is found high among bipolar patients and it needs public health attention.