Introduction: Knee osteoarthritis belongs to the most frequent diseases of modern time and it is the main cause of chronic disability, reduced flexibility, productivity, pain and reduced quality of life. Its frequency increases with age due to the prolonged life expectancy and frequency of obesity. Obesity is the main risk factor for development of knee osteoarthritis. Purpose: The purpose of the literature review is to present the effects of body mass reduction on reducing pain in the knee joint with knee osteoarthritis. Methods: We used a descriptive method with a review and analysis of technical and scientific literature. We searched literature written in the English language in PubMed and PEDro databases with key words »knee osteoarthritis« and »loss weight«. We used a time frame in our search, namely the period between 2009 and 2020. Results: Five randomized control researches, corresponding to all inclusion and exclusion criteria, were included in the literature review. The loss of more than 10 % of body mass causes significant reduction of body mass and pain, regardless of the type of diet. Body mass reduction and improvement of symptoms led to a more active lifestyle and lesser medicine consumption. Reducing body mass can alleviate the symptoms in any phase of the disease. Those who reached excessive body mass in the early childhood showed a greater risk for lower limbs osteoarthritis. The group on a diet loses more body mass than the group working out. Patients suffering from knee osteoarthritis are less active due to pain and consequently losing body mass for them is more difficult. Discussion and conclusion: Appropriate body mass should be one of the top priorities already in the early childhood. Children should be even more informed about the appropriate daily physical activity, a healthy diet and a healthy lifestyle. It is necessary to act properly already before the occurrence of symptomatology and the first signs. When knee osteoarthritis occurs in an overweight patient, treatment must be directed towards body mass reduction and working out. It is important to raise awareness of healthcare workers and patients about the significance of appropriate body mass in the development of knee osteoarthritis.