It is so called inception motion of sediments when sediment particles begin to move in a flow. So far numerous studies have been performed about the determination of inception motion of uniform non-cohesive sediments in the open channels with the positive slope and relations or graphs in this topic have been presented however, there are a few studies about inception motion of non-uniform non-cohesive sediments in the channels with the negative slope. In this research, conditions of inception motion of non-uniform non-cohesive sediments were investigated by using a laboratory flume and dimensional analysis. The 9 samples of non-uniform non-cohesive sediments with different size and uniformity coefficient at three positive slopes 0/0005, 0/001, 0/002 and three negative slopes, 0.0005, 0.001, 0.002 were examined in this experiment. Results showed that by increasing the positive slope, the stability parameter of particle reduces and by increasing negative slope, the stability parameter of particle increases. Moreover, results showed that by increasing particle size parameter, particle stability parameter reduces and
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