The aim of the present study was to determine the effects of three weeks of hyperbaric oxygen (HBO 2 ) training on oxidative stress markers and endurance performance in young soccer players. Participants (<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" id="M1"><mml:mn fontstyle="italic">18.6</mml:mn><mml:mo>±</mml:mo><mml:mn fontstyle="italic">1.6</mml:mn></mml:math> years) were randomized into hyperbaric-hyperoxic (HH) training (<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" id="M2"><mml:mi>n</mml:mi><mml:mo>=</mml:mo><mml:mn fontstyle="italic">6</mml:mn></mml:math>) and normobaric normoxic (NN) training (<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" id="M3"><mml:mi>n</mml:mi><mml:mo>=</mml:mo><mml:mn fontstyle="italic">6</mml:mn></mml:math>) groups. Immediately before and after the 5th, 10th, and 15th training sessions, plasma oxidative stress markers (lipid hydroperoxides and uric acid), plasma antioxidant capacity (6-hydroxy-2,5,7,8-tetramethylchroman-2-carboxylic acid [TROLOX]), arterial blood gases, acid-base balance, bases excess (BE), and blood lactate analyses were performed. Before and after intervention, maximal oxygen uptake (VO 2 max) and peak power output (PPO) were determined. Neither HH nor NN experienced significant changes on oxidative stress markers or antioxidant capacity during intervention. VO 2 max and PPO were improved (moderate effect size) after HH training. The results suggest that HBO 2 endurance training does not increase oxidative stress markers and improves endurance performance in young soccer players. Our findings warrant future investigation to corroborate that HBO 2 endurance training could be a potential training approach for highly competitive young soccer players.