The aims of this study were (1) to determine how stair-climbing-based exercise snacks (ES) compared to moderate-intensity continuous training (MICT) for improving cardiorespiratory fitness (CRF), and (2) to explore whether ES could improve maximal fat oxidation rate (MFO) in inactive adults. Healthy, young, inactive adults (n:42, age: 21.6±2.3 years, BMI: 22.5±3.6kg·m-2, peak oxygen uptake (VO2peak): 33.6±6.3mL·kg-1·min-1) were randomly assigned to ES, MICT, or Control. ES (n=14) and MICT (n=13) groups performed three sessions per week over 6 weeks, while the control group (n=15) maintained their habitual lifestyle. ES involved 3 × 30s "all-out" stair-climbing (6 flight, 126 steps, and 18.9m total height) bouts separated by>1 h rest, and MICT involved 40min×60%-70% HRmax stationary cycling. A significant group×time interaction was found for relative VO2peak (p<0.05) with ES significantly increasing by 7% compared to baseline (MD=2.5mL·kg-1·min-1 (95% CI=1.2, 3.7), Cohen's d=0.44), while MICT had no significant effects (MD=1.0mL·kg-1·min-1 (-1.1, 3.2), Cohen's d=0.17), and Control experienced a significant decrease (MD = -1.7mL·kg-1·min-1 (-2.9, -0.4), Cohen's d=0.26). MFO was unchanged among the three groups (group×time interaction, p>0.05 for all). Stair climbing-based ES are a time-efficient alternative to MICT for improving CRF among inactive adults, but the tested ES intervention appears to have limited potential to increase MFO.