The purpose of this study is to examine the effect of 30-minute duration submaximal running and roller skiing exer- cises, which are among the most important aerobic exercise models in cross-country skiers, on lactic acid levels. The study group comprised 6 female and 4 male athletes (age: 16.87±1.87years, body height: 168.35±5.66 cm, body weight: 56.83±7.1kg) who competed in cross-country skiing at national and international level. All athletes participated in the study voluntarily. Measurements were performed three times as basal (1st measurement), immediately after exercise (2nd measurement) and 5 minutes after finishing exercise (3rd measurement).Statistical analysis was conducted using SPSS (version 11.5). A significant increase (P<0.01) in lactic acid levels was found for both 30-minute submaximal exercise types; however, this effect did not differ statistically between groups. Running exercises caused greater fatigue than ski- ing exercises, according to percentage values, but the difference in fatigue levels between exercise types was not statisti- cally significant