Firefighting requires high fitness to perform job tasks and minimize risk of job-related cardiac death. To reduce this risk, the International Association of Firefighters has recommended firefighters possess a VO2max ≥ 42 ml·kg-1·min-1. This recommendation is not universally applied because existing screening tests require costly equipment and do not accommodate firefighters unable to run. The purpose of this study was to develop a walking test to predict VO2max in firefighters using a standard treadmill. Thirty-eight male firefighters wore a vest weighing 20% of their body weight and performed a walking VO2max test on a standard treadmill. Walking speed was dependent on leg length and ranged from 3.6 to 4.3 mph. The test began with a 3-minute warm-up, after which the speed was increased to test speed. Every minute thereafter, the grade increased 1% until participants reached exhaustion. For cross-validation, 13 firefighters also performed a running VO2max test. The average test time was 16.95 ± 2.57 minutes (including warm-up) and ranged between 8 and 22 minutes. Average VO2max was 48.4 ± 6.5 ml·kg-1·min-1. Stepwise linear regression included time as the only significant independent variable explaining 76% of the variance in VO2max (p < 0.001). The standard error of the estimate was 3.2 ml·kg-1·min-1. The equation derived is: VO2max (ml·kg·min-1) = 11.373 + time (minute) × 2.184. On average, VO2max values measured while walking were 4.62 ± 5.86 ml·kg-1·min-1, lower than running values. This test has good potential for predicting VO2max among structural firefighters, and minimal equipment needs make it feasible for fire departments to administer.