Prolonged work in upright postures (standing and walking) is common in industry and in daily living activities, and is one possible risk factor for low back pain and leg problems. This study compared the reaction forces of four different floor surface conditions (three inner-room floor mats and no-mat) during gait. The reaction forces were measured by both the in-shoe and platform type pressure measurement systems. Six male subjects (average weight = 72.4 +/- 7.5 kg) walked barefoot on the four floor conditions and the data from the two measurement systems were recorded simultaneously. The mean reaction force, two peak forces (heel strike and toe off), and the maximum reaction force measured by the in-shoe type system showed significantly different values according to the floor surface conditions (P < 0.05). The no-mat condition induced the largest mean reaction force of 828.9 +/- 114.2 N, However there was no difference in the reaction forces measured from the platform type system (P > 0.05). All three floor mats induced smaller reaction forces than no-mat, but the mean reaction force and maximum reaction forces (maximum and two peak forces) showed different results due to different thickness and materials. Thus, an appropriate selection of inner-room floor mat according to the biomechanical properties may be useful for reduction of fatigue and discomfort in industrial settings.