An experimental study of partially submerged bidisperse granular column collapse on a flat bed is conducted in this paper. The effect of the particle size and particle composition, as well as the interstitial water on the collapsing process are investigated. A total number of 55 experimental cases are observed by varying the particle size, the finer-particle fraction, and the saturation level, i.e., the ratio of the initial height of the interstitial water level to the total height of the initial column. It is shown that the mobility of partially submerged bidisperse columns increases as the particle size difference increases, while decreases as the finer-particle fraction increases. Effect of the interstitial water on the collapsing process is somewhat complicated. It retards the granular flow at the acceleration stage of the collapse but enhances the granular flow at the deceleration stage in an overall sense. The final run-out of a partially submerged bidisperse column depends not only on the saturation level, but also on the size of the finer particles in addition to the finer-particle fraction. The particle segregation observed during collapse, however, is less affected by the saturation level.