Background: COVID-19 is a highly contagious new virus infection. The World Health Organization officially declared it a public health emergency on January 30, 2020. Its progression may be influenced by human behavior, which is affected by knowledge and perceptions. Individuals may be affected by its physical, psychological, and social repercussions. Fear is a psychological consequence affecting individuals, especially older adults. People need to be well-informed and adopt protective behaviors to dispel this fear and halt the infection's spread. Aim: Assess and compare COVID-19 related fear, knowledge, and protective behaviors among middle-aged and older Adults. Research design: A cross-sectional comparative research design was employed. Setting: The study was conducted at the Specialized Medical Hospital outpatient clinics affiliated with Mansoura University Hospitals. Subjects: A convenience sample of 246 patients; 123 were aged 20 to less than 60 years (middle-aged), and 123 were 60 and older (older adults) were eligible to participate in the study. Tools: Four tools were utilized: Demographic Characteristics and Health-related Data Structured Interview Schedule, Fear from COVID-19 Scale, COVID-19 Knowledge Questionnaire, and Self-reported COVID-19 Protective Behaviors Checklist. Results: Both the middle-aged and older adult groups had poor knowledge of COVID-19 (46.3% & 56.9%, respectively) and had unsatisfactory COVID-19 protective behaviors (55.3 % and 64.2%, respectively). As for the comparison between both groups, there was a statistically significant difference between middle-aged and older adult groups (p=0.000*) in which the older adult group had a lower level of knowledge, unsatisfactory health behaviors, and higher level of fear related to COVID-19 than middle-aged group (16.422±7.794, 20.211±6.731); (20.430±5.502, 23.813±4.123); (11.853±4.698, 21.325±6.327), respectively. Conclusion: The study's findings concluded that both age groups had poor knowledge, unsatisfactory health behaviors, and fears related to COVID-19. At the same time, the older adult group had lower mean scores of knowledge and health behaviors and higher levels of fear related to COVID-19 when compared with the middle-aged group. Recommendations: There is an urgent need for public health education through instructional programs for different age groups in Egypt to correct misconceptions and improve their knowledge and protective behaviors regarding COVID-19, as well as alleviate distressing feelings and fear.