Re-formation process of alternate bars caused by the deformation of meandering streams which developed from alternate bars and effects of water discharge on it are investigated by means of flume tests using the uniform and the non-uniform sediment. Experimental results show that widening of meandering streams is caused by the erosion of emerged bars when the sediment supply rate is same as the sediment transport rate, whereas it is caused by both the erosion and the riverbed aggradation when the former is larger than the latter. Alternate bars are formed easily in the non-uniform sediment bed because the emerged bars in the bed are eroded easily than those in the uniform sediment bed. The bed with meandering streams is transformed into large-scale alternate bar bed by riverbed aggradation and low water discharge.