Type 2 diabetes (T2D) is characterized by reductions in β-cell function and insulin secretion on the background of elevated insulin resistance. Aerobic exercise has been shown to improve β-cell function, despite a subset of T2D patients displaying "exercise resistance". Further investigations into the effectiveness of alternate forms of exercise on β-cell function in the T2D patient population are needed. We examined the effect of a novel 6-week CrossFit™ Functional High Intensity Training (F-HIT) intervention on β-cell function in 12 sedentary adults with clinically diagnosed T2D (54±2 years, 166±16 mg/dL fasting glucose). Supervised training was completed 3 days a week, comprising of functional movements performed at a high intensity in a variety of 10-20 minute sessions. All subjects completed an oral glucose tolerance test and anthropometric measures at baseline and following the intervention. The mean Disposition Index (DI), a validated measure of β-cell function, was significantly increased (PRE: 8.4±3.1, POST: 11.5±3.5, P=0.02) after the intervention. Insulin processing inefficiency in the β-cell, expressed as the fasting proinsulin-to-insulin ratio, was also reduced (PRE: 2.40±0.37, POST: 1.78±0.30, P=0.04). Increased β-cell function during the early-phase response to glucose correlated significantly with reductions in abdominal body fat (R²=0.56, P=0.005) and fasting plasma alkaline phosphatase (R²=0.55, P=0.006). Mean total body fat percentage decreased significantly (: -1.17±0.30%, P=0.003), while lean body mass was preserved (: +0.05±0.68kg, P=0.94). We conclude that F-HIT is an effective exercise strategy for improving β-cell function in adults with T2D.