Despite observed ethnic differences in eating patterns and obesity, evidence in China is limited. This study examined ethnic differences in eating patterns and their associations with weight outcomes among multi-ethnic adults in West China. A cross-sectional survey collected self-reported data on demographics, eating behaviours, weight and height in 2021. Principal component analysis and multivariate regression were conducted to identify eating patterns and examine their associations with weight outcomes. In total, 4407 subjects aged ≥ 18 years were recruited across seven provinces in West China. Four eating patterns were identified: ‘meat-lover’ – characterised by frequent consumption of meat and dairy products, ‘indulgent’ – by frequent intakes of added salt, sugar, alcohol and pickled food, ‘diversified-eating’ – by frequently consuming food with diversified cooking methods and eating out and ‘nutri-health-concerned’ – by good food hygiene behaviours and reading food labels. Ethnic differences in eating patterns were observed. Compared with Han, Hui were less likely to exhibit meat-lover or diversified-eating patterns; Tibetans were less likely to have meat-lover or nutri-health-concerned patterns; Mongolians were more likely to have indulgent pattern. BMI was positively associated with meat-lover pattern in both genders (exp(β): 1·029; 95 % CI: 1·001, 1·058 for men; 1·018; 1·000, 1·036 for women) and negatively associated with nutri-health-concerned pattern in women (0·983; 0·966, 1·000). Mongolians were two times more likely to be overweight/obese than Han (OR: 3·126; 1·688, 5·790). Considerable ethnic differences existed in eating patterns in West China. Mongolians were more likely to be overweight/obese, which was associated with their indulgent eating patterns. Ethnic-specific healthy eating intervention programs are needed.