While some studies suggest that a linear dose-response relationship exists between exercise and insulin sensitivity, the exercise dose required to enhance pancreatic beta-cell function is unknown. Thirty-five older, obese adults with prediabetes underwent a progressive 12-week supervised exercise intervention (5d/wk for 60min at ~85% HR_max). Insulin and C-peptide (n=23) responses to an OGTT were used to define the first and second phase disposition index (DI; beta-cell function = glucose-stimulated insulin secretion x clamp-derived insulin sensitivity). Maximum oxygen consumption (VO₂max) and body composition (dual-energy x-ray absorptiometry and computed tomography) were also measured before and after the intervention. Exercise dose was computed using VO₂-heart rate derived linear-regression equations. Subjects expended 474.5±8.8 kcal/session (2372.5±44.1 kcal/week) during the intervention, and lost ~8% body weight. Exercise increased first and second phase DI (P<0.05), and these changes in DI were linearly related to exercise dose (DI_{first phase}: r=0.54; P<0.001 and DI_{second phase}: r=0.56, P=0.0005). Enhanced DI was also associated with increased VO₂max (DIfirst phase: r=0.36; P=0.04, DI_{second phase}: r=0.41, P<0.02), but not lower body fat (DIfirst phase: r=-0.21; P=0.25 and DI_{second phase}: r=-0.30, P=0.10) after training. Low baseline DI predicted an increase in DI after the intervention (DI_{first phase}: r=-0.37 and DI_{second phase}: r=-0.41, each P<0.04). Thus, exercise training plus weight loss increased pancreatic beta cell function in a linear dose-response manner in adults with prediabetes. Our data suggest that higher exercise doses (i.e. >2000 kcal/week) are necessary to enhance beta-cell function in adults with poor insulin secretion capacity.