Objectives:To explore obesity prevalence and its association with dietary patterns among Tibetan pastoralists during the urbanization transition in Qinghai Province.Methods:Using an open cohort study design, 1 003 subjects were enrolled at baseline in 2018, 599 were followed up, and 1 012 were newly recruited in 2022. A total of 1 913 adults over 18 years were included in the study, and a questionnaire survey and health examination were conducted. Factor analysis was used to identify dietary patterns, and a mixed-effects model was used to analyze the association between dietary patterns and obesity.Results:From 2018 to 2022, the prevalence rates of overweight, obesity, and central obesity were 27.6%, 33.8%, and 54.6%, respectively. Age-sex-standardized prevalence of obesity and central obesity increased. Three dietary patterns were identified: the modern pattern was characterized by frequent consumption of pork, poultry, processed meat, fresh fruits, sugary drinks, salty snacks, etcetera; the urban pattern was characterized by frequent consumption of refined carbohydrates, beef and mutton, vegetables and eggs, etcetera; and pastoral pattern featured frequent consumption of tsamba, Tibetan cheese, buttered/milk tea, and whole-fat dairy products. After adjusting for demographic characteristics, socioeconomic status, and lifestyle factors, compared with the T1, subjects in the T3 of urban pattern scores were more likely to be overweight ( OR=2.09, 95% CI: 1.10-3.95) and overweight/obese ( OR=1.23, 95% CI: 1.00-1.51), whereas those in the T3 of pastoral pattern scores had a lower risk of overweight ( OR=0.45, 95% CI: 0.24-0.84), obesity ( OR=0.81, 95% CI: 0.69-0.95), overweight/obesity ( OR=0.75, 95% CI: 0.61-0.91) and central obesity ( OR=0.58, 95% CI: 0.38-0.89). Conclusions:Prevalence of obesity and central obesity was high among Tibetan pastoralists during the urbanization transition. Urban dietary pattern was a risk factor for overweight and overweight/obesity, whereas pastoral dietary pattern was a protective factor for overweight, obesity, overweight/obesity, and central obesity. Tailored interventions are needed to improve local people's health.