Background: Competent, good and safe intensive and critical care nursing is based on the knowledge, attitudes and values, experiences and skills of the ICU nurses. So, employing interested and competent nurses and considering the standards required in the ICU can increase the quality of care. The purpose of the study: Investigate the relationship between nurses‟ competencies and quality of patient care provided at intensive care units. Study design: A descriptive co-relational design was used to carry out this study. Study setting: The study was conducted in the intensive and intermediate care units at Menoufia University Hospitals. Study sample: A convenient sample of 145 staff nurses and 145 critically ill patients, taken care of by the studied nurses. Data collection instruments: The first instrument was a modified version of the Intensive and Critical Care Nursing Competence Scale. The second instrument was the patient‟s care quality observation checklist. Results: The present study showed that more than half of the studied nurses (54.5%) had good level of competency and it was associated with good total knowledge level (88.2%), positive attitudes (97.2%) and satisfactory level of practice (95.9%). The study results illustrated that the majority of the studied patients (61.4%) had moderate level of quality of patient care. There was no statistical correlation between socio-demographic characteristics of the studied nurses and total competency level and also those of the studied patients and total quality of care level (p>0.01). Conclusion: There was a highly statistical significant positive correlation between the competency of nurses and the quality of patient care at Intensive Care Units. Recommendations: Competence should be assessed regularly in clinical practice to explore individual learning needs for continuing education to improve the quality of health care.