Disclosed is a refractory coating composition, which includes: based on the total weight of the composition, (a) 20 to 40 wt % of cement, (b) 15 to 40 wt % of ground-granulated blast-furnace slag, (c) 5 to 20 wt % of at least one selected from among mica and alumina, (d) 0 to 10 wt % of flyash from a fluidized-bed boiler, (e) 10 to 40 wt % of expanded vermiculite, (f) 10 to 30 wt % of at least one selected from among calcium carbonate and limestone, and (g) 0.5 to 20 wt % of a thickening agent, and which also has a predetermined porosity and thus an appropriate density, is non-shrinkable to thus reduce cracking due to shrinkage, and exhibits drastically increased resistance to heat in the event of a fire.