Objective:To compare two Nutrition and Health Surveys in Taiwan (NAHSITs) 15-18 years apart to evaluate secular changes in ultra-processed food (UPF) consumption and expenditure among Taiwanese adolescents aged 16-18 years and the influences of such changes on dietary quality. Design:This cross-sectional study was based on two representative surveys (NAHSIT 1993-1996, n = 788; NAHSIT 2011, n = 1,274) of senior high school students. Dietary information and food expenditure were based on 24-h dietary recall. All food items were classified into original foods, processed culinary ingredients, processed foods, and UPFs based on NOVA criteria. Dietary quality was categorized as poor or good based on the mean of the Youth Healthy Eating Index-Taiwan Revised. Results:Compared to 1993-1996, adolescents consumed less energy from original foods (55 vs. 39%) but more from processed foods (12 vs. 18%) and UPFs (21 vs. 25%) in 2011, with no apparent gender differences. Those who consumed more UPFs had the lowest proportions of protein energy intake in both surveys (13.7 and 13.1%). Those who consumed more UPFs had higher levels of saturated fat and lower levels of monounsaturated and polyunsaturated fat, dietary fiber, and micronutrient intakes. The participants who consumed more UPFs and fewer original foods exhibited poorer dietary quality. Boys and girls exhibited equal UPF expenditure in both surveys despite an increase in UPF energy consumption. The adjusted odds ratios (95% confidence interval) were 1.33 (1.16-1.52) and 1.36 (1.10-1.69) for the risk of poor dietary quality with 10% increases in UPF energy intake and expenditure, respectively, in 2011. Conclusions:UPF energy consumption among Taiwanese adolescents increased between 1993-1996 and 2011. Observed trends in expenditure suggest that lower UPF costs influenced food choices during this period. Increasing UPF intake and expenditure was associated with poor dietary quality.