Falling is a serious threat for patient safety in hospitals. This study aimed to identify the risk factors of fall amongst rehabilitation patients and to use them for developing and validating the Persian version of Fall Risk Assessment Scale (FRAS). The current methodological study was conducted in two phases. In the first phase, based on the review of the literature and investigation of the medical records of 251 patients selected via purposive sampling, the risk factors of fall were extracted and the FRAS was developed accordingly. In the second phase, the face and content validities of the designed scale were determined by cognitive interview and Content Validity Index (CVI) and to evaluate the construct validity, known-groups comparison was performed. Its inter-rater reliability was analyzed using the weighted Kappa Coefficient (κ*). The study adhered to COSMIN guidelines. Fall was significantly associated with disease diagnosis, used medications, history of fall, cognitive impairments, and three items of the Functional Independence Measure (toilet transfer, bed transfer, and shoer transfer). The CVI of the scale was 0.94. The risk for falls group had a significantly higher perceived fall risk than the no risk for falls group, thus establishing known-group validity. Its weighted kappa coefficient was >0.85, its sensitivity was 73%, and its specificity was 82%. The valid and reliable FRAS may accurately assess the level of Fall Risk patients in Rehabilitation wards, helping to predict fall during hospitalization. So, enabling the planning and implementation of effective caring interventions.