A stair climbing experiment was performed using a four‐stair instrumented stairway. A force platform was mounted in the first stair. Four floor surfaces, including the original force platform surface and three additional floor coverings on the platform, were tested. Human subjects wore the same type of lab shoes and ascended and descended the stairway. Their ground reaction forces were collected. The results showed that when descending, the double‐stair condition resulted in significant (p < .0001) higher vertical ground reaction force at foot landing as compared to the single‐stair condition. The vertical ground reaction force at foot push‐off for stair ascent were significantly (p < .0001) higher than those for stair descent. The mean required coefficient of friction ranged from 0.086 to 0.245 and from 0.051 to 0.246 for foot landing and foot push‐off spots, respectively. Stair descent required significant (p < .001) higher friction than stair ascent both at foot landing and push‐off. Double‐stair stepping required higher friction than single‐stair stepping. Stair descent should be of primary concern in assessing the risk of slip‐ and fall‐related incidents on stairway, and double‐stair descent should be avoided.