To provide an ultrafine particle grouting composition which is excellent in dispersibility and dispersion retainability and can be easily injected into minute spaces between particles of grounds, rock cracks, and the like. An ultrafine particle grouting composition comprising ultrafine particle cement, wherein the ultrafine particle grouting composition is at least one selected from the group consisting of the following (i) and (ii): (i) the ultrafine particle grouting composition comprises ultrafine particle cement (A) and a polycarboxylic acid dispersant (C), and the ultrafine particle cement (A) comprises blast furnace slag and gypsum, andthe ultrafine particle cement (A) has 10% by volume or less of particles having a particle diameter of 16 .mu.m or more in powder form of the cement; and (ii) the ultrafine particle grouting composition comprises ultrafine particle cement (B) and a polycarboxylic acid dispersant (D), and the ultrafine particle cement (B) comprises 2 to 25% by weight of cement clinker containing 5% by weight or less of 3CaO.Al.sub.2O.sub.3, 74 to 97% by weight of blast furnace slag, and 1 to 5% by weight of gypsum, and the ultrafine particle cement (B) has 60 to 80% by volume of particles having a particle diameter of 1 to 5 .mu.m in powder form of the cement.