The present invention relates to a self-leveling aqueous composition comprising 100 parts by weight of a base material which is a mixture of cement and natural type-II anhydrous gypsum which are mixed in a weight ratio from 40/60 to 80/20, 0.1 to 3 parts by weight of an acrylic dispersant or a dispersant mixture which contains 0.1 to 3 parts by weight of an acrylic dispersant and 0.1 to 2 parts by weight of a melamine dispersant; 0.01 to 0.6 parts by weight of a thickener; 0.01 to 0.6 parts by weight of a defoaming agent; 0.05 to 1 part by weight of a setting accelerator; 0.2 to 6 parts by weight of a shrinkage inhibitor; 30 to 300 parts by weight of an aggregate; and 30 to 60 parts by weight of water.; The self-leveling aqueous composition has excellent characteristics in that it generates only very little changes in length, does not generate cracks or separate from the substrate, and has high waterproofing performance, without being affected by environmental conditions or thickness of the installation. In addition, it maintains a high fluidity for a long period. Accordingly, it is possible to manufacture the composition in a factory, and transport it to the working site by an agitator truck for pouring on the substrate. Thus, the compositions of the present invention are excellent from the viewpoints of quality and working efficiency.