Purpose: The 6 min walk test (6MWT) is used in clinical and epidemiological practice as a simple tool to evaluate the maximal aerobic exercise capacity (VO2max). To date, little evidence has been provided regarding regression equation models to predict VO2max in older adults. Therefore, the main purpose of the study was to develop a reference equation to estimate objectively measured VO2max, based on the 6MWT, sex, age and body mass index (BMI). Patients and Methods: In this observational prospective study, we collected the data from 233 asymptomatic participants aged 60–80 years (52.4% women). VO2max and the 6MWT were measured using standardized protocols. BMI was calculated as weight (kg) divided by height squared (m2). To be able to develop the predictive equation for VO2max, we used linear generalized estimating equations (GEE). Results: Older men performed better in VO2max (30.9 ± 8.8 vs. 26.3 ± 6.3 mL/kg/min,p< 0.001) and the 6MWT (673.9 ± 58.7 vs. 642.3 ± 48.0 m,p< 0.001), compared to women. VO2max was correlated with the 6MWT (r= 0.71,p< 0.001), sex (r= −0.29,p< 0.001), age (r= −0.62,p< 0.001) and BMI (r= −0.38,p< 0.001). The model to predict VO2max included: VO2max (mL/kg/min) = 59.44 − 3.83 *, sex (1—men; 2—women) − 0.56 *, age (years) − 0.48 *, BMI (kg/m2) + 0.04 *, and the 6MWT (m) (R= 0.85;R2= 72.3%,SEE= 3.99 mL/kg/min,p< 0.001). Conclusion: The newly developed regression equation can be a guideline in clinical and epidemiological practice to predict the VO2max in apparently healthy older adults.