Elite women volleyball players (n=25; age; 19±5 yrs, height; 171±7 cm, weight; 63±10 kg; means±SD) volunteered to participate in the study. They were randomized into a high intensity training group (HIT; n=13) and a control group (CON; n=12). In addition to the normal team training and games, HIT performed 6-10x30-s all-out running intervals separated by 3-min recovery periods 3 times per wk during a 4-wk in-season period, while CON only completed team training sessions and games. Pre and post intervention all players completed the Arrowhead Agility Test (AAT), a repeated sprint test (RST; 5x30 m separated by 25 s of recovery), and the Yo-Yo Intermittent Recovery level 2 test (Yo-Yo IR2) followed by a-10 min rest period and the Yo-Yo IR1 test. Mean running distance during HIT-training in wk-1 was 152±4 m and increased (P<0.05) by 4.6% (159±3 m) in wk-4. AAT performance improved (P<0.05) by 2.3% (18.87±0.97 to 18.44±1.06 s) and RST by 4.3% post-intervention in the HIT-group only. Baseline RST fatigue index (FI) was 7.0±2.9 and 6.2±5.0% in HIT and CON, respectively, but was lowered (P<0.05) to 2.7±3.0% post-training in HIT and remained unaltered in CON (5.5±5.0%). In HIT, Yo-Yo IR2 and Yo-Yo IR1 performance improved by 12.6 and 18.3% post-intervention, respectively, with greater (P<0.05) change scores than in CON. In conclusion, additional high intensity in-season training performed as interval running improved agility, repeated sprint ability and high intensity intermittent exercise performance in elite women volleyball players.