Many bed load equations based on dimensional analysis and experiments have proposed. But one which is applicable on mountain streams have not been established. Recently the authors have studied on flow resistance and sediment transport on steep slope channels with uniform and nonuniform bed materials. In this paper, first we derive a new bed load equation for uniform grains based on Bagnold's model and make it applicable for steep slope channels. Secondly, bed load of sand mixtures are considered. Carrying out experiments about the critical condition for the stopping of sand mixtures, we find that the critical shere stress for each size grain stopping is constant and is nearly equal to the value for mean diameter. Based on this fact, a new bed load equation for sand mixtures is derived and it fits experimental results very well. Alternation of grain size distribution with time is also discussed. These results are applicable for mountain streams.