INTRODUCTION: Obesity is among the most common diseases of modern civilization. The World Health Organization (WHO) describes obesity as one of the major public health challenges of the 21st century, and it is defined as too much fat in the body. Physical activity and exercise play an important role in the overall approach to treatment, but also in prevention of obesity. RESEARCH OBJECTIVE: The main objective of this research is to check the connection of organized exercise with the level of body mass index and the speed of performing the Timed Up and Go test to obese people. In addition to the main objective of the research, two specific objectives were defined: compare the improvement in the levels of body mass index in obese people who practice after 55 days of exercise and compare the improvement in the speed of performing the Timed Up and Go test to obese people who practice after 55 days of exercise. SUBJECTS AND METHODS: Respondents to the study are patients who visit the Obesity clinic and participate in physical activity conducted 2 times a week in the premises of the Faculty of Health studies in Rijeka. The data necessary for conducting the study were collected by measuring the height and body weight of the subjects and their speed of performing the Timed Up and Go test. Data analysis includes descriptive statistics, calculation of Spearman correlation coefficient and t-test for dependent samples, at significance level p < 0,05. MedCalc Free Trail was used for statistical data processing. RESULTS: It has been shown that there is no statistically significant association of organized exercise with the level of body mass index and the speed of performing the Timed Up and Go test to obese people. Also, a statistically significant difference in the level of body mass index after 55 days of exercise was demonstrated, as well as a statistically significant difference in the speed of performing the Timed Up and Go test after 55 days of exercise. CONCLUSION: Physical activity and organized exercise have a positive effect on decreasing the obesity in the world. It is necessary to raise awareness among the world's population of the many consequences of obesity, as well as to encourage physical activity and exercise.