This study compared the two step heights (35 cm vs. height adjusted according to the 90° knee angle) on the predictions of the □O2max predicted with their step indexes (SI) and steady heart rates (HR) during the test. Twenty-one college male students were the subjects (age: 21.71+0.45 years old, height: 174.7±7.1cm, weight: 69.9±8.1kg, □O2max: 45.41±1.30 ml/kg/min). □O2max was measured by the cycle ergometer with increasing workload. Participants performed respectively twice the step test which were divided into Fixed Height (FH: 35 cm) and Modified Height (MH: modification of the step height based on 90° knee angle). The frequency of the step test is 24 step/min for 3 minutes. The heart rate during exercise was measured to estimate HR, and the heart rate after exercise was measured to estimate SI. The results were as follows: First, correlation analyses between □O2max and the □O2max predicted by SI-FH and SI-MH were in significant (r=.469, p<.05; r=.681, p<.05). Second, correlation analyses between □O2max and the □O2max predicted by HR-FH 及HR-MH were significant (r=-.626, p<.05; r=-.582, p<.05). Third, there was no difference between measured □O2max and predicted □O2max by SI-FH, SI-MH, HR-FH and HR-MH (p>.05). The correlation between □O2max and the □O2max predicted by SI of MH was higher than that of FH. The correlation between □O2max and the □O2max predicted by HR of FH was higher than that of MH. The step height adjusted according to the 90° knee angle can improve the validity to predict □O2max.