Flow unsteadiness in flood events has a significant effect on the structure of the flow field and motion of sediment particles, thereby affecting dispersion of pollutants and river ecology. The aim of the present article was to evaluate state-of-the-art research efforts concerning flow characteristics and sediment transport in unsteady flow condition. The paper is organized in four sections: The first section deals with the unsteady parameters which affect sediment transport. In the second section, the flow characteristics in unsteady open channel flow are presented. Different studies showed that the flow characteristics which affect sediment transport including velocity distribution or shear stress during passage of a hydrograph differ from steady flow condition. In addition, measurements during passage of a hydrograph show that turbulence intensity is generally larger in the rising limb of the hydrograph rather than in the falling limb. This causes the peak of sediment load and pollutants occur during the rising limb of the storm hydrograph. The third and forth sections deal with bed load and suspended load in unsteady flow condition, respectively. Studies show that the methods which are based on steady flow conditions generally underestimate the sediment transport rates in unsteady flows. The larger the unsteadiness, the bigger is the difference. Finally, with considering different findings from previous studies, suggestions are presented for further research.