(1) To examine the comparability, i.e., discriminatory power, in a preschooler test (PREFIT 20-m shuttle-run test) and the 20mSRT-Original in 5-6-year-olds; (2) to provide an equation to estimate VO(2)max from the 20mSRT-PREFIT. 138 participants aged 5-6 years performed the 20mSRT-PREFIT and the 20mSRT-Original in a counterbalanced order. Total test duration, completed stages, maximum speed and maximum heart rate were registered. Participants finished stages from 2-10 in the 20mSRT-PREFIT, whereas stages 1-5 were completed in the 20mSRT-Original and a null was registered, showing the original version a lower discriminatory power. We also observed that the higher the cardiorespiratory fitness level the more comparable were the tests, i.e., – 0.04 km h(-1) difference between tests in the fittest participants (i.e., maximum speed ae 9.5 km h(-1)). Using the original equation proposed by Leger and colleagues in 1988 and based on the estimation regression of maximum speed in the 20mSRT-Original from the PREFIT version, we computed a new equation to estimate VO(2)max from the 20mSRT-PREFIT: Y = 44.657 + 1.795X (1) – 2.601X (2) + 0.0852X (1) X (2) (r = 0.77; r (2) = 0.59; SEE = 1.25 ml kg(-1) min(-1) or 2.59% of estimated mean VO(2)max = 48.38 ml kg(-1) min(-1)), where X (1) is the 20mSRT-PREFIT maximum speed (km h(-1)) and X (2) is the age of participants. The 20mSRT-PREFIT resulted in a significantly higher maximum heart rate than the 20mSRT-Original. The 20mSRT-PREFIT has higher discriminatory power than the 20mSRT-Original. Our study provides for the first time an opportunity to estimate VO(2)max in preschoolers and children based on the 20mSRT-PREFIT maximum speed and the age of participants.