PURPOSE: An additive for coal-water slurry having excellent effects of enhancing stability on standing and fluidity, prepd. by incorporating an adduct of an active hydrogen-contg. compd. with ethylene oxide, etc. and an unsaturated monocarboxylic acid copolymer, etc.

CONSTITUTION: About 30W95wt% polyether compd. (deriv.) obtd. by addition of ethylene oxide (alkylene oxide may be used together) to an active hydrogen- contg. compd. is compounded with about 70W5wt% at least one component selected from among an unsaturated monocarboxylic acid/unsaturated monocarboxylic acid amide (or unsaturated monocarboxylate) copolymer(salt) and an ethylenesulfonic acid/styrene (or maleic anhydride or acrylic acid) copolymer (salt), to prepare an additive for coal-water slurry. Said additive is added to the coal-water slurry (coal concn.: about 30W85wt%) in a proportion of about 0.01W 5wt% based on the slurry for use.