Introduction: Length of stay is one of the most important and most practical indices used in hospitals today and presents the performance and efficiency of the hospitals. On the other hand, hierarchical analysis technique, one of the group decision making techniques, is utilized to determine priorities. Therefore, this study was conducted to identify the factors affecting length of stay in Alzahra Hospital based on hierarchical analysis technique. Methods: This descriptive cross-sectional survey included the management, chief, educational supervisor, and also nursing and ward managers of Alzahra Hospital in Isfahan during 2009. All the subjects were selected by census sampling method. Data collection tool was the paired comparisons questionnaire. Data analysis was done by Expert Choice software. Results: Generally, patient's underlying disease (0.245), availability of beds (0.203), being discharged before holidays (0.657), coordination between paraclinical and treatment units (0.294), health personnel's awareness (0.241), performing various graphies in the hospital (0.286), and nurses' sympathy with the patients (0.517) were the most effective factors on length of stay. Conclusion: Identifying the factors effective in shortening the length of stay is one of the main responsibilities of hospital managers. Factors related to patient visit, coordination with other sectors and patient characteristics are the most important and need more planning and attention from hospital officials. Keywords: Length of Stay; Analyic Hierarchy Process; Presonnel, Hospital.