A gelling agent comprising an organopolysiloxane having a silicon-bonded organic group represented by general formula: R1—X—CO—NH—[X—N(—CO—X—R1)]p—X— (1) (wherein R1 designates a group containing metal salt of a carboxylic acid represented by formula —COO− (Mn+)1/n (where M is a metal that has a valence of 1 or higher); X's designate the same or different C2 to C14 bivalent hydrocarbon groups; and p designates an integer from 0 to 10.). Preferably, the organosiloxane has an optionally substituted C9 or more univalent hydrocarbon group. And a gelatinous composition comprising:(A) 1 to 99 wt. % of aforementioned gelling agent; and (B) 99 to 1 wt. % of a compound selected from the group consisting of a silicone oil, a no-polar organic compound, or a low-polar organic compound, or mixtures thereof. The gelatinous composition has excellent thermal stability, temporal stability, and properties of thixotropic rheology.