Background: Hand hygiene before and after each contact with any patient, is simple, easily implemented and an effective practice to prevent hospital acquired infection.This study aimed to  assess the knowledge, attitude and practice of hand washing among health care workers (HCW) in health care units in Arar city, Northern Saudi Arabia, based on WHO's ‘Five Moments of Hand Hygiene Questionnaire'. Methodology: A descriptive cross sectional study was carried out at health care unites in Arar city during the period from July to September 2017. The World Health Organization (WHO) "Hand Hygiene Knowledge Questionnaire"- revised 2009 edition was used. Results: In total, 116 respondents including 32 residents, 92 nurses and 37 nursing assistants enrolled in this study,68% of them were females and 32% were males, 41% were resident, 32.8% nurses, 12.9% Nursing assistant and 12.9% Technician. The mean score of HH knowledge in residents technicians, nurses and nurse assistants was 18 (±1.8), 17.7(±1.7), 18.3(±1.2) and 18.1(±1.4) respectively. While the mean score of attitude was the highest in nurses 6.9(±1.17) then the technicians 6.8(±1.6), and the lowest score was found in the nursing assistants 6.2(±0.56). The  mean score of practice was found to be 4(±1.6) in technicians, 3.9(±1.0) in nurses, 3.8(±0.9) in residents and 3.5(±0.6) in nurse assistants. The majority of the participants (90.5%) had a high level of knowledge of HH. The attitude level was found moderate in 81.9% and high in only 17.2%. Level of practice of HH was high in 23.3%, moderate in 75.9% and almost none of our participants was found with a low level of practice.  Conclusion: This study highlighted the importance of applying the multimodal training program addressing providers' knowledge regarding hand hygiene, as well as strategies for emotional and behavioral methods such as patient engagement in hand-hygiene interventions.