||Sleep is essential for rest, repair, well-being, and survival of the patient. Sleep quality varies in critically ill patients and is measured by patient's satisfaction of the sleep experience, integrating aspects of sleep initiation, sleep maintenance, quantity of sleep and the refreshment upon awakening. Altered sleep is a common problem experienced by patients in critical care units. This alterations may lead to physiological and psychological dysfunctions that may affect recovery. Critically ill patients frequently experience poor sleep, characterized by frequent disruptions and loss of circadian rhythms. This study investigated factors influencing the quality of sleep among critically ill patients in hospitals in Western Kenya. A cross-sectional descriptive research design was used to examine these factors. A total of 142 patients above 18 years who were admitted to the Intensive Care Unit (ICU) and those transferred from the ICU to the general ward during the study period were conveniently selected for participation in the study. For triangulation, 10 nurses who worked in the ICU also participated in the study. A structured questionnaire was used to collect data from patients while a checklist was used to observe nursing interventions. Descriptive statistical techniques used were frequencies and percentages, while chi-square was used with the p-value set at 0.05 to test the association between factors and quality of sleep. The study results showed that frequent, nursing care activities 96.5% (n=137) noise from ventilator alarms 83.1% (n=118), feeling thirsty 57.7% (n= 82) and pain 52.8% (n=75) were among the major factors influencing the quality of sleep in ICU. A one-way analysis of variance (ANOVA) revealed patient factors significantly associated with quality sleep were age p=.006 and marital status p=.02, environmental factors significantly affecting sleep were presence of light at night with a p <0.0001 and noise from alarms p=.01. Physiological factors included feeling of thirst and hunger (p=0.03). This study recommends optimal use of analgesics and sedatives for pain management, adequate fluid replacement and hydration, noise reduction strategies, including minimizing monitor and ventilator alarms, reducing staff and telephone conversations and use of ear plugs for patients in ICU. Further, nurses should implement clustered procedures to reduce disruption of sleep among critically ill patients.