Background: Intensive Care Unit Acquired Muscle Weakness (ICU-AW) is one of the most important complications occurs in the ICU. ICU-AW is a multifactorial syndrome characterized by generalized muscle weakness. Critical care nurses (CCNs) have an important role in the prevention of ICU-AW through increase mobility and applying of range of motion. Design: A descriptive exploratory design was utilized to achieve aim of this study. Aim: This study aimed to assess factors contributing to acquired muscle weakness among critical ill patients. Setting: the study was carried out in intensive care units of Beni-Suef University Hospital. Subjects: A Purposive sample of seventy five patients admitted in the previous mentioned setting. Tools of data collection were consisted of Patient assessment tool, muscle strength scale and indicators to incidence of ICU-AW and factors contributing to ICU-AW assessment tool. Results: revealed that more than half of the studied patients had ICU-AW. The majority of studied patients who had muscle weakness were older than the Non ICU-AW patients. Application of positioning and range of motion exercises were not done in the ICU-AW patients. Administration of corticosteroid and incidence of malnutrition was higher in the ICU-AW patients than the Non ICU-AW patients. There were no statistically significant relation between incidence of ICU-AW and gender, admission medical diagnosis, administration of parenteral nutrition and application of positioning and walking exercises. Conclusion: More than half of studied patients developed ICU-AW. The contributing factors of ICU-AW are patient age, WBCs level, not applying range of motion and chair sitting exercise to ICU patients, administration of corticosteroid and malnutrition. Recommendations: Further researches are recommended to study extensively the effect of nutritional status on incidence of ICU-AW. Also, examine the incidence of ICU-AW in sedated and unconscious patients.