A dispersant comprises a polystyrenesulfonic acid having a weight-average molecular weight in the range of 2,000 to 100,000 or a salt thereof, wherein at least 70% of the terminals of the polymer chain have an indane ring of the formula (I): ##STR1## wherein X represents a cation selected from the group consisting of a hydrogen, alkali metals, alkaline earth metals, ammonium and organic amines, and n and m each represent 0 or an integer of at least 1. The dispersant has excellent properties of dispersing organic and inorganic substances and an effect of remarkably improving the stability of a dispersion system such as a coal/water slurry.