Road pavement reflectance is usually assumed to be invariant in short periods of time in some quantitative remote sensing applications. To examine its variability, reflectance sequences of concrete and asphalt pavement are measured in field for half a day in visible and near-infarecd (VNIR) spectral range using dual-beam method. As much as 20.7% and 3.52% of relative changes are found in asphalt and concrete reflectance data at 550 nm, and all VNIR bands demonstrate similar variations found to correlate with both illumination geometry and the relative portion of diffuse irradiance. In this letter, this effect is interpreted from a mathematic view. Further studies are needed to model the dynamics of reflectance physically.