Background: Katz Index is a well-known index for assessing basic activities of daily living. The aim was to determine validity and reliability of the Katz Index in Iranian patients with acute stroke. Methods: Eighty-seven patients (56 male, 31 female) with acute stroke (1-30 days post-stroke) participated in this psychometric properties study. Interval time for retest was 14 days. All participants were Iranian with Persian as native language, had no other major diseases (e. g. cancer, Alzheimer) and no psychiatric disorder. Cognitive mental score of all participants was above 18 (according to Mini-Mental State Examination). If they had another stroke during the following-up period, they were excluded from the study. Intraclass Correlation Coefficient (ICC), Standard Error of Measurement (SEM) and Minimum Detectable Change (MDC) were calculated to investigate the reliability of the KI. Criterion validity of the KI was assessed by Spearman’ s Correlation Coefficient (ρ ). Moreover, Confirmatory Factor Analysis (CFA) and Exploratory Factor Analysis (EFA) were performed to investigate the construct validity of the KI. Results: Inter-rater and intra-rater reliability of Persian Katz Index were reasonable (ICC2, 1=0. 93, ICC2, 1=0. 83; respectively). Internal consistency of this index was high (cronbach’ s alpha=0. 79). The high to excellent correlation was found between Katz Index and the motion (ρ =0. 88), self-care (ρ =0. 98), and total scores (ρ =0. 92) of Barthel Index. Factor analysis of the Persian Katz Index indicated two factors including motion (bathing, toileting, and transferring) and self-care (dressing, bowel & bladder control, and feeding). Conclusion: The results of this study suggest that Persian version of Katz Index in patients with acute stroke can be considered as an acceptable clinical instrument in practice and research.