Purpose: Long-distance running performance has been reported to be associated with sprint performance in highly trained distance runners. Therefore, we hypothesized that sprint training could enhance distance running and sprint performance in long-distance runners. This study examined the effect of 6-week sprint training on long-distance running and sprint performance in highly trained distance runners. Methods: Nineteen college runners were divided into control (n = 8) and training (n = 11) groups. Participants in the training group performed 12 sprint training sessions in 6 weeks, while those in the control group performed 12 distance training sessions. Before and after the interventions, maximal oxygen uptake (${\dot{\mathrm{V}}\mathrm{O}}_2\text{max}$), O₂ cost during submaximal running (290 m·min⁻¹ and 310 m·min⁻¹ of running velocity), and time to exhaustion (starting at 290 m·min^–1 and increased 10 m·min^–1 every minute) were assessed on a treadmill. Additionally, the 100-m and 400-m sprinting times and 3000-m running time were determined on an all-weather track. Results: In the control group, no measurements significantly changed after the intervention. In the training group, the time to exhaustion, 100-m and 400-m sprinting times, and 3000-m running time improved significantly, while ${\dot{\mathrm{V}}\mathrm{O}}_2\text{max}$ and O₂ cost did not change. Conclusions: These results showed that 6-week sprint training improved both sprint and long-distance running performance in highly trained distance runners without a change in aerobic capacity. Improvement in the time to exhaustion without a change in ${\dot{\mathrm{V}}\mathrm{O}}_2\text{max}$ suggests that the enhancement of long-distance running performance could be attributable to improved anaerobic capacity.