OBJECTIVES: This study examined the effect of maturation on parasympathetic nervous system (PNS) response from rest to light- to moderate-intensity exercise and recovery from maximal exercise in pre- (n = 10; maturity offset = -3.0 +/- 1.2 years; age = 10.1 +/- 1.9 years), mid- (n = 9; maturity offset = -0.1 +/- 0.6 years; age = 13.7 +/- 1.0 years), and postpubertal (n = 10; maturity offset = 1.9 +/- 0.6 years; age = 15.6 +/- 1.2 years) boys and men (n = 10; age = 24.1 +/- 2.0 years). DESIGN: Participants completed seated rest, light-intensity exercise (50% HR(max)), and moderate-intensity exercise (65% HR(max)). Following moderate-intensity exercise, intensity was ramped to elicit maximal HR and followed by 25 min of seated recovery. Log transformed values for root mean square of successive differences (lnRMSSD), high-frequency power (lnHF) and normalized HF power (lnHFnu) assessed PNS modulation during 3 min of rest, light-intensity exercise, moderate-intensity exercise, and 3-min epochs throughout recovery. RESULTS: During light-intensity exercise, lnRMSSD and lnHF were greater in prepubertal (lnRMSSD = 3.4 +/- 0.3 ms; lnHF = 5.4 +/- 0.7 ms(2)) compared to men (lnRMSSD = 2.8 +/- 0.5 ms; lnHF = 4.0 +/- 0.9 ms(2)). During moderate-intensity exercise, lnHF differed between prepubertal and men (2.8 +/- 1.0 vs. 1.4 +/- 1.0 ms(2)). During recovery, HRV variables were greater in prepubertal compared to postpubertal and men. CONCLUSIONS: Prepubertal boys have reduced PNS withdrawal during light-intensity exercise and greater PNS reactivation following exercise.