One of the critical problems in making an effective strategy to control road dust emission is to estimate the emission factor accurately. A wind tunnel was built in the laboratory to measure the emission factor of road dust under different wind acceleration conditions. Test road dusts were collected from two sites, one from the construction site where a DRAM factory was being constructed in the Science Industrial Park of Hsin-Chu (dust sample # 1) and the other from an unpaved road at Nan Laio area of Hsin-Chu (dust sample #2). The dust samples were first sieved using a standard No. 325 mesh to remove particles greater than 44 pm. Thereafter, the dust samples were dried and then contained within an aluminum cell of 5 (width) x 5 (length) x 0.2 cm (depth), which was embedded in a working platform in the wind tunnel. The surface of dust samples was kept flush with the plate before testing. Test results show that the air acceleration rate affects the emission factor significantly. As the air acceleration rate is increased from 0.1 to 1.5 m/s(2), the emission factor is increased linearly from 1.0 to 7.0 x 10(-4) kg/m(2)-s for sample #1, and from 0.1 to 1.0 x 10(-4) kg/m(2)-s for sample #2. Test results show that the air acceleration rate has no significant effect on the threshold wind speed for reentrainment, which was found to be 10-12 m/s for sample #1, and 9-10 m/s for sample #2. While the edge effect at the surface of the dust sample has no significant effect on the threshold wind speed for reentrainment, it increases both reentrained dust concentration and emission factor significantly.