There is provided a gelator that is capable of forming a gel by an extremely small amount of addition in a wide pH range from acidic to alkaline regions, and a gel having high environmental compatibility, biocompatibility, and biodegradability. A gelator comprising: a lipid peptide of Formula (1) wherein R 1 is a C 9-23 aliphatic group, R 2 is a hydrogen atom or a C 1-4 alkyl group optionally having a C 1-2 branched chain, R 3 is a -(CH 2 ) n -X group, n is a number from 1 to 4, and X is an amino group, a guanidino group, a -CONH 2 group, or a 5-membered ring optionally having 1 to 3 nitrogen atoms, a 6-membered ring optionally having 1 to 3 nitrogen atoms, or a fused heterocycle including a 5-membered ring and a 6-membered ring that optionally has 1 to 3 nitrogen atoms)； or a pharmaceutically usable salt of the lipid peptide.本發明可提供在酸性至鹼性之液性範圍，可形成極少量膠體之膠化劑、以及具有高度之環境‧活體適合性及生物分解性之膠體者。本發明係以式(1)(式中R1示碳原子數9至23之脂肪族基、R2示氫原子，或可具有1或2碳原子數之支鏈的碳原子數1至4之烷基，R3示-(CH2)n-X基，n示1至4之數，X示胺基、胍基、-CONH2基，或由具有1至3個氮原子之五節環或六節環或由五節環與六節環所構成之縮合雜環)所示之脂質肽或其藥學上可使用之鹽為特徵的膠化劑。
