Exercise training is effective for improving cardiometabolic health and physical fitness in inactive adults. However, limited research has been conducted on the optimal exercise training intensity for this population. We investigate the effect of moderate versus high intensity interval exercise training on vascular function and physical fitness in physically inactive adults. Twenty inactive adults were randomly allocated to receive either moderate intensity training (MCT group) or high intensity interval training (HIT group). The MCT group performed aerobic training at an intensity of 55-75% of the walking on a treadmill at 60-80% heart rate max (HRmax) until expenditure of 300 kcal until the end of training. The HIT group performed running on a treadmill during 4 minutes at 85-95% peak HRmax and had a recovery of 4 minutes at 65% peak HRmax until expenditure of 300 kcal until the end of training. Vascular function (flow-mediated vasodilation, FMD [%], aortic pulse wave velocity, PWV [m·s−1]), blood lipids [fasting glucose, triacylglycerol, total cholesterol, LDL-cholesterol, HDL-cholesterol], blood pressure, and physical fitness (Muscle strength (handgrip [kg]), exercise capacity (V̇O2peak and graded exercise test duration [minutes]), were measured at baseline and 12-weeks thereafter.Trial registration. ClinicalTrials.gov NCT02738385, registered on 23 March 2016.